I do know that there are enthusiasts who make Garmin compatible maps and then provide them for no cost to the masses. I found one for Greece that had very good coverage for Corfu, though it didn't have things like restaurants, gas stations, etc.

I have attempted to put some of my Crotia destinations in my Garmin.

It's not 100% good. I am staying in Rovinj. Garmin apparently doesn't go there LOL!

However, I still think it will be useful enough to take.

I don't know what paper maps exist for Croatia, but even if you can't get digitized street maps, you can use a GPS to locate yourself (approximately) on the paper one.

A $70 unit will do that - like this one I got for #3 son: woot.com/Blog/BlogEntry.aspx?BlogEntryId=1608