I searched Barnivore for chocolate liqueur and it only came up with a listing for Godiva liqueurs which aren't vegan. Kahlua has some vegan options, like I think the Mocha has chocolate in it?:
http://barnivore.com/liquor/73/KahluaIf you know of any other companies that produce it you should email them and find out if they're vegan and submit the results to Barnivore!