[SVAuspicious]

I need an ASA 104 certificate to bareboat for 1 week in Croatia next September.

Testing out is the right answer. You may find that working with a sailing school is the best way to find an ASA instructor to work with you on your own boat. Give Sailtime, Annapolis Sailing School, and MD School for Seamanship a call and lay out your desires. Can't hurt, might help.

Good luck.