I would also add that female tinctorius and male pumilios (as well as other species) will fight and intimidate one another to the point where you'll lose the less dominant frog(s) eventually. I've never had terrilibus, but have heard that they do well in groups. I would imagine a group of males would work. They are also one of the most bold dart frog species.

Another option would be to get a pair that someone has had for a few years that has never successfully bred. My first pair of azureus (see avatar) are three years old and stopped producing eggs two years ago. The female suffered some kind of seizures a while ago and seems to have lost the ability to produce eggs. She is perfectly healthy, but I doubt she'll every produce eggs again. I'm not saying that I'd want to part with the pair, but I am also running out of room and could use the viv they are in for a breeding pair.