There is none, in that a lot of the modern definitional terms used to define capitalism really do have their origin in Marx and Marxian writing. After all, the Marxists were first and foremost describing the society which they lived in before going on to elaborate their proposals for something different (which Marx himself was notoriously actually vague about).

What might come closest is writing by the Classical Liberal economists and their advocacy for unregulated ("Free") economic markets, who described and advocated for the policies which would little under a century later lead to the social conditions in turn described by Marx and Engels. The Classic Liberal authors which might interest you would probably be Adam Smith ("Wealth of Nations") David Ricardo ("On the Principles of Political Economy and Taxation," although parts on Comparative Advantage are only the ones that you need to look at for lasting impact on economic thought) and if you really want to dive deep, Jean-Baptiste Say's commentaries on Adam Smith (which notably challenge Smith's advocacy of the Labor Theory of Value — a theory which would be picked up again by the Communists — and instead argued in favor of a strictly utilitarian price interpretation).

The thing is, all these texts are pretty dense and what they fundamentally do is very verbosely espouse the principles which to this day mark the foundation of modern economics (even for Marxists, who don't really challenge the mechanical principles of free market economics, but really only pass a moral and social judgement on the consequences of that free market). What the authors intend to do by espousing these principles is to demonstrate the increased prosperity that would be brought about by a freer economy, and thus advocate for drastically changing the heavily-regulated Early Modern Economy, which even at the time of their writing still featured laws very much favoring agricultural land ownership to the detriment of commerce and emergent industry, and with a big slice of commerce itself managed by state-sponsored or otherwise heavily regulated organizations. So what I'm getting at is these works don't really serve the purpose of a "counterweight" to Marx; they very much are "Predecessors" to Marx in the chronology of economic ideas. You can find a mechanical summary of these ideas in pretty much any introductory economics textbook.

So what would I propose is "Equivalent" to Marx on the other end of the spectrum? I have no idea; maybe the answer is some "Gospel of Wealth" book published sometime in the '80s. But I can’t name any writer who vehemently disagreed with Marx and sat down to write down an equally influential work looking to disprove his ideas, or wrote a work defending the status quo as described by Marxian analysis. But I do sort of have an answer for you! There is a very (academically) influential work, possibly outdated nowadays and not uncontroversial, which does explicitly look at Marx's analysis and offers significant counter-commentary: "Capitalism, Socialism, and Democracy" by Joseph Schumpeter (this is, at long-last, my answer to your question). In Schumpeter's analysis, the capital-owning class is not entirely parasitic as Marx instead insists, but is instead described as serving as the conduits of "Creative Destruction," a concept which would gain a lot of steam among self-described "capitalists." Schumpeter goes on to draw conclusions about economics, society, and politics which are very different to Marx's, and in many ways describe the workings of our own modern sociery.

But at the end of the day, you probably do not imagine a self-described capitalist pointing at passages of Schumpeter's works (probably because Schumpeter ultimately comes to the same conclusion as Marx and believes that Capitalism eventually destroys itself, even if he argues method by which that destruction is achieved is different). If you think about it, politicians and pundits who rave on the wonders of capitalism do not wave a book, pamphlet, or manifesto around. Why? Why is there no "Capitalist Manifesto?"

I think it is because Capitalism (as we understand it nowadays) is best understood as a "Thing That Exists;" it has no single ideation, no identifiable progenitor. I threw my hat in a number of discussions linked to, "What is Capitalism, really?" which might interest you and offer a bit more color on the idea for you:

• This short answer of mine from about a month ago, where I link to several other posts to try to answer, "How old is Capitalism?" (the answer is, well, under most definitions it has existed as long as humans have traded things)

• This answer from six months ago where I ramble a bit on "The Origin of Capitalism."

• This other answer from six months ago where I try to explain that a lot of the chronology and terms linked to "Capitalism" actually come from Marxian/Marxist analysts.

• This sort-of long-winded answer from three months ago about the industrial revolution, where I briefly try to clarify the tools of Marxian analysis (among other things)

I would suggest Albert Hirschman "Passion and Interest: Arguments in Favor of Capitalism Before Its Triumph" and Ha-Joon Chang "Economics: A User Guide". They are not a straight out opposition, but they provide the strengths of capitalism.

Hirschman is left-leaning economist who were part of the generation where the economics is a field of the humanity rather than a social science. He was born in Europe, and immigrated to the US, during WW2. Seeing the living standards of people in "communist" nations, it is not hard not to prefer capitalism. The book is written as reminder of when capitalism is considered an alternative to feudalism and how the back-and-forth arguments continued. Marx' s argument is also mentioned but not refuted. Hirschman is the type of scholar who prefer the reader to make their own conclusion.

In that book, Hirschman cited many authors. Many of whom would be what you looking for. They are, after all, supporters of capitalism. And you would also find authors that would be more closely aligned to Marxist thinking.

Ha-Joon Chang simply describe the economy of the world, the different theories of how it work and the how they applied. It is a very simplified version but overall, Ha-Joon Chang said that "Capitalism is a terrible system but it is better than every other system that has been tried". Whatever problems he had with it (and he had more than plenty, since he is known for attacking it rather than a supporter), he provide enough reasons to why he prefer it over others.

I hated to recommend books I did not read directly but seeing arguments from them in many books or praises from their oppositions are work by Robert Nozick, "Anarchy, State and Utopia" and Hayek " The Roads to Serfdom". You may want to check it out. They are in my will-read list but not a pro. Many respected authors who I knew, disagreed with them, respect these books rather than trash them sparked my interest.

A short classic that I highly recommended is "Exit, Voice and Loyalty" by Albert Hirschman. Like most of Hirschman' s works, he did not demand any cause of actions. That book is a description of the mechanics in why economists promoted capitalism and why political scientists promoted state interference. It is personally, became my go-to arguments against both capitalism and socialism.