What airlines are available to fly from Venice, Italy to Drobrovic, Croatia? Do we need to buy the tickets in the USA? Would it be cheaper to take the ferry from Ancona?
Larry, I'm assuming you mean Dubrovnik (DBV). I did a quick search on Kayak.com and it looks like the only airline flying direct between DBV and Venice Marco Polo (VCE) is Austrian Airlines.
http://www.flylc.com/from/en/ap-dbv.htm shows all the budget airlines that fly in and out of DBV. I don't see any other direct flights, but I bet you could find a connecting flight.
Good luck!