I saw somewhere that "Gog" mentioned in the Torah is Greece. Does anyone know a source for this?
I don't think there is Gog mentioned in the Torah. There is however Magog in parshas Noach.
In Yechezkel 38 2 Rashi and Radak says Gog is king of Magog. Radak says Magog is from Yefes, Malbim also connects them to Yephes through Tuval mentioned there. Yefes is classically associated with Greece, Rabbi Kaplan brings some identifying Yefes with the Greek Iapetus.
(Rabbi Kaplan though does not being any opinions connecting Magog specifically to Greece.)