Hi i think it will depend where you are going, i've been to Rovinj, Porec & Umag and have been able to find them usually in the little kiosks. You can not get all brands though. I paid £22 for 200 last September but they may have gone up.
Remember you can buy at the airport (dutyfree) when going to Croatia.
Hope that helps a little:)

You can buy them in every store and kiosks in Croatia.
Prices:
Croatian cigarettes:
Ronhill, Ronhill lights, Ronhill superlights: 15 kunas, I recommend
Walter wolf (blue), WW lights: 14 kunas
Avangard: 19 kunas (only gay people and women smoke them in Croatia)
Largo, Benston, Columbo, Filter 160: 11 kunas ONLKY SMOKE THEM IF YOU'RE VERY DRUNK AND HAVING A CRISES, VERY SHITTY CIGARETTES, BAD TASTE IF YOU'RE NOT SMOKING THEM SINCE YOU WERE 7..

Foreign cigarettes:
Marlboro: 20 kunas
Kent: 21 kunas
Lucky strike: 20 kunas

You'll find these in most of the markets, other brand only in tobacco shops
Be aware! It is still allowed in Croatia to smoke in all public places, but they are preparing the new law so ask around when you get there.

Oh yeah, 1 pound is 9,3 kunas

The ones i was writing about are Dunhill International, last year they were 22 kuna for 20.