Give me a call on 0031 70 512 5227 or firstname.lastname@example.org
I know Croatia really well and can get you access to any number of Croatian boatyards and english speaking Croatians (I work with about 350 Yugoslavs).
Another possibility is that I have a 5M rib that you could collect from The Netherlands (I'm 20mins from Hook of Holland) and tow down to Croatia. Depending which part you are going to depends on which route, but northern Croatia in a day is possible (but tiring). Other parts and you need to take the Ancona to Split or Zadar or Dubrovnik ferry.
Be warned: I wanted to hire a RIB for a few days once and was presented with a monster which I rejected. I then had to get one of my chums to sort outthe whole mess.
Have you decided upon your destination yet?
I hope to be of help.
Briton in exile