You could find a regular camping gas stove in all town's in Montenegro without any problem. In Podgorica the capital you have this camping gas stove in almost all small shops.

Pierceable gas cartridges are sold everywhere, but screw-in cartridges are hard to find. I've seen screw-in cartridges in the center of Zabljak, in the VOLI supermarket, at the second floor:



These are rather large (500 g).