Yoel 4 says:
3 And they have cast lots for My people; and have given a boy for an harlot, and sold a girl for wine, and have drunk.
and
6 the children also of Judah and the children of Jerusalem have ye sold unto the sons of Jevanim, that ye might remove them far from their border;
The King James bible says that "Jevanim" is Greece.
When did this happen in history to the Jewish people?
One of the problems with the book of Joel is that it lacks any information that might locate it historically, and a number of pronouncements within it are ambiguous for that reason (eg: is the army in chapter 2 being likened to a plague of locusts, or is the plague of locusts in chapter 2 being likened to an army?). Rabbinic tradition has it that the author was the son of Samuel the prophet (Bemidbar Rabbah 11), but since so much of the book is concerned with events that are yet to transpire, that doesn't really help us.
The section to which you refer is one such passage. Note that it commences by asserting what will happen in those days (בימים ההמה), which the Radak interprets to mean the time of the moshiach. If, in the time of the moshiach, people are to be punished for the things that they had done, those things may not have yet transpired in human history - certainly not at the time of the prophet, and perhaps not yet from our perspective either.
An indication of this ambiguity can be found also in the Radak, who mentions two interpretations of this passage: one, that it happened while the Judeans were still residing in their land; and the other, that it happened after the destruction of the temple when they were in exile. By contrast, the Malbim sees it as something that happened during the time of the temple's destruction itself. Since the passage is so vague, it could have happened at any time, or could also be something that has not (yet) happened at all.
