Putting aside that I don’t consider 10 b/c to be “easy”, for multi-pitch in Croatia you can’t pass up Anica Kuk in Paklenica. It is the most impressive, most iconic peak in the range, with routes to match, approaching 1000ft. for the longest routes, with a quite easy approach and straightforward walking descent. While the route that we did, Mosaraski (9/10a?), is easier that your desired range, it was still a good route ( but for a short bit of loose rock in the middle), but it’s near neighbor Velebitaski is supposed to be a classic and right in your target range.
When we were there, over a decade ago, we needed some gear to supplement the very well spaced bolts, but it wouldn’t surprise me if the climbs were now more well-bolted—or you are likely bolder than we were. I’m sure that you can get more up-to-date information on the bolting situation with a bit of on-line ‘digging’.
On the way to Anica Kuk, starting just past the parking lot, you go through the narrow gorge called Klanci, which is the location of a very dense collection of mostly single-pitch sport routes on either side, directly above the wide cobble-stoned trail, which gives you a choice of sun or shade depending on the conditions ( don’t know when you will be going, but it gets hot that far south—Anika is in the shade for much of the day).
I have not climbed elsewhere in the country, so can’t give you any further recommendations. One other thing, though, the grades, at least in Paklenica, very much tend to be on the stiff side, at least a letter grade, often more, off of the norm in most other parts if Europe.
It is a fascinating country. Enjoy your visit.