Were the philosophers of Ancient Greece aware of Eastern Philosophies, such as Zoroastrianism or Buddhism? Is there any mention of them, either directly, or similar concepts in existing writings?
I don't remember any references but Zoroastrianism was known.
"The religion named after him is not attested to historically until the 5th century BCE, where it appears in Greek sources."
Zoroaster's name in his native language, Avestan, was probably Zaraϑuštra. His English name, "Zoroaster", derives from a later (5th century BCE) Greek transcription, Zōroastrēs (Ζωροάστρης), as used in Xanthus's Lydiaca (Fragment 32) and in Plato's First Alcibiades (122a1). This form appears subsequently in the Latin Zōroastrēs and, in later Greek orthographies, as Zōroastris.
Although, at the core, the Greeks (in the Hellenistic sense of the term) understood Zoroaster to be the "prophet and founder of the religion of the Iranian peoples" (e.g. Plutarch Isis and Osiris 46-7, Diogenes Laertius 1.6–9 and Agathias 2.23-5),
Zoroastrianism enters recorded history in the mid-5th century BCE. Herodotus' The Histories (completed c. 440 BCE) includes a description of Greater Iranian society with what may be recognizably Zoroastrian features, including exposure of the dead.
And in this article about the "Hellenistic" period (~300 BC) there are some info about Greek interactions in far east
Several philosophers, such as Pyrrho, Anaxarchus and Onesicritus, are said to have been selected by Alexander to accompany him in his eastern campaigns. During the 18 months they were in India, they were able to interact with Indian ascetics, generally described as Gymnosophists ("naked philosophers"). Pyrrho (360-270 BC) returned to Greece and became the first Skeptic and the founder of the school named Pyrrhonism. The Greek biographer Diogenes Laërtius explained that Pyrrho's equanimity and detachment from the world were acquired in India. Few of his sayings are directly known, but they are clearly reminiscent of śramanic, possibly Buddhist, thought: "Nothing really exists, but human life is governed by convention. ... Nothing is in itself more this than that"
Another of these philosophers, Onesicritus, a Cynic, is said by Strabo to have learnt in India the following precepts: "That nothing that happens to a man is bad or good, opinions being merely dreams. ... That the best philosophy [is] that which liberates the mind from [both] pleasure and grief".