instea as well as Judaism was around from the outset of Iron Age Greece.
Philosophers such as Xenophanes(?), Anaxagoras, Plato and Aristotle believed in some sort of monotheism.
Alexander the Great was supposedly partial to Judaism (see from Alexander to Jesus by Ory Amitay) also echoed here on a Jewish website.
So I'm wondering. Since Isaiah was written around 800BC if the idea of monotheism was independently derived by Greece or if they had unknowingly borrowed the ideas from the Levant.
Edit: I am thinking that the ideas were developed independently and might be a natural evolution of ideas (ironically an idea I combatted with ever since playing Sid Meier's Civ games). That monotheism might just be a natural byproduct of polytheism. I've read some theories that Yawyeh was part of the Canaanite pantheon initially and evolved into a type of monotheism similar to how Hinduism and Egyptian faiths evolved into a type of Godhead theism which culminated in one deity being promoted over the others until it arrived at a type of monotheism.
However, the close proximity of the Levant with Asia minor has me wondering if instead the idea was instead borrowed vs internally derived.
I'm not really sure going off the type of sources you are looking for and there's a bit of debate about how monotheistic you want to call these thinkers especially Xenophanes (it's a pretty debated topic whose debate is helped a great deal by the fact we just do not have very much from him to work off of), but I think i can help. i'm going to restrict my argument to something simple: did any ancient thinkers agree with you? Yes: Philo of Alexandria.
Philo, the middle platonist sees Moses as the first in the line of philosophers continuing on to Plato and Aristotle. The forms become god's ideas (arguably the first time this happens).
Also as my source below notes the "the books of the prophets [later books of OT] bring us up to the time of the earliest presocratic philosophers" i.e. Temple falls in 538 BC aka during the lifetime of pythagarus. it's not really an argument for or against you it's just helpful to put the long range of the writings in perspective.
Similarly Numidius of Apamea famously asked "what is plato but moses speaking in Attic Greek"
Here is a "history of philosophy" podcast on Philo (run by philosophy professor and i would highly recommend if you are looking for a brief overview on lots of major and especially minor philosophers).
http://www.historyofphilosophy.net/philo-alexandria
hope this helped