It depends on what kind of music we're talking about! You wouldn't go around to shop for an orchestral score, you would probably buy keyboard scores for your daughters. A score is, for the common user (not a composer who uses sheet music to study), meant to be played, and most people didn't have an orchestra in their living room. The sheet music that was being printed in a larger quantity was thus either keyboard or vocal scores. During the 19th century especially, it was increasingly popular for the growing European bourgeoisie to have a piano (bigger and more expensive than a guitar, still feasible for a household) as a status symbol and as a leisure activity. In a sense, keyboard scores had a similar function as recorded music.

The precise availability of orchestral scores is beyond my knowledge, though.

In his biography of Johannes Brahms, Jan Swafford claims that Brahms was the first composer who was able to make a living solely doing his own work, without having to do any commissions. I'm not sure how accurate that part is, but one key to Brahms' success was his reliance on selling sheet music. He sold music for his songs, chamber works, and for some of his larger pieces he actually transcribed them for four-hand piano.

He also took his Requiem and transcribed it so it could be played by four hands on the piano and sung by a small vocal group--partly as an exercise, but mostly to get it ready for printing.

So at least one 19th century composer was selling enough sheet music to make a good living.

Maybe /u/caffarelli has more information?

I can partly answer your question regarding transcriptions. Yes there were transcriptions that were being published around Europe and yes they varied in quality, and in some cases "quality" changed with the performance philosophy of the day.

Here's an example of Mozart's Piano Concerto no. 5, K.175 (written originally for piano with orchestral accompaniment) transcribed for solo piano (published in Paris in 1785), and two harpsichords (published sometime in the 18th century after 1773, in Italy maybe?).

When judging quality in a transcription, aside from legibility, you'd also be looking at authenticity because a lot of the times editors would throw in their own musical markings. Ferruccio Busoni is notorious for doing this and his 19th century editions of Bach's Well Tempered Clavier are filled with markings that Bach himself never put. At the time this was accepted because piano was starting to be mainstream and people had no idea how to interpret Bach's music. But today, it'd be considered unprofessional to play a Busoni edition for a performance because the expectation is to play and interpret a score which resembles Bach's manuscripts.

Another thing, that score for solo piano I linked above would be considered outdated and inaccurate. Page 12 "Allegretto grazioso", is actually cataloged under K.382 and is part of a completely different piece.

I'm not sure of the time period you're referencing, but I do have a stack of guitar sheet music almost as tall as me and while none of it is itself old, a lot of it is transcribed from historical printings and often they will include interesting bits from the original printings.

Fernando Sor was a virtuoso guitarist and composer in the 19th century who published many works which were eventually compiled into a volume which I purchased online some years back for $24.95 if I paid what the sticker says.

I scanned some of the cover pages, and it's interesting to see that it was popular enough that in the preface to one book he'd reference feedback he'd gotten on previous books regarding difficulty, pricing and such.

Album is here

For a related question, we always hear about countless examples of both literature and cinema having been permanently lost. Are there any well known examples of music that has been lost? Particularly in the form of piano sheet music similar to the orchestras that made the likes of Mozart famous?

Alois Sennefelder, inventor of lithography, describes in his "History of the Art of Lithography" 1819, having perfected his new printing method, but finding no market for his own theatrical writings, he considered abandoning lithography when he writes:

"A page of wretchedly printed music from a prayer-book which I accidentally met with at a shop at Ingolstadt, suggested to me the idea that my new method of printing would be particularly applicable to music printing;..."

Immediately following this preamble, Sennefelder describes quick success printing and selling numerous copies of topical sheet music, and most importantly, quickly: "in a fortnight composing, writing on stone, printing and selling 120 copies for 100 florins netting 70 florins profit." In 1796. Sennefelder continues with a short history of sheet music lithography, including a profitable 150 copies of an ode on the death of Mozart.

Sennefelder drones on about his failures and frustrations as well. Namely, his quick profitable operation did not go unnoticed and others started mass lithography of sheet music, and other printing too, by, he claims, stealing his invention.