I don't think there are crossbows in hexographica, although you can get plenty of other nifty medieval units from that tagset (pikes, cavalry, ballistas, catapults). There was a crossbow unit in an old map called (I think) Deathtrap, but it looked pretty terrible. The only other crossbowman I've ever seen is the one in TFV (since you're a beta tester, Zeph, that might be what you're remembering), but it isn't available for public use yet.
Are you saying Myth 2's bowmen are not human? :O :;):
Is there a reason you need a crossbow type instead of the old bow and arrow type? Or its just for a variety?
Matthew J Redding's "Megalithic" was the source for that crossbowman. Speaking of units, I'm going to post my list of units in the General Forum in a few minutes.