I've read Apollonius, Pindar, and Ovid's Metamorphoses, and I haven't found that version yet. (Unless of course I'm an idiot whose mental abilities have been exhausted beyond repair by her research paper.) I've seen references, but I can't figure out what the primary source for it is.
Edited to keep you updated: so far, the one line of Sophocles' Colchian Women I have been able to find is, of Ganymede, "Inflaming with his thighs the royalty of Zeus."
Um, I think this is a sign it's time to work on other things for the night.