I read in a book that the only north american ants that tropical frogs will eat is the flying ants, because the others produce that acidic thing that tastes bad to the frogs. I actually read it in my mantella's book, but I am sure it applies to most tropicals. Anyway, Good luck,
I would search for "ants" on this board as this topic has come up before. As far as info on the kinds of ants and how to get them, check out http://www.tincs.com They have some info in their gadgets section.
Well depending on where you live you may have more suitable species then others. Doing alot of research on the subject and asking MANY questions to many ant hobbiest, and found out the majority of Florida's ant species are suitable for the darts consumption. One that all of us will beable to have is the pesty black ants that you see all the time and get into orchid baskets all the time! So if anyone interested if you live in Florida the big headed ants(not all have big heads only certain ones whcih are called the majors) are suitable. I can find them verry easily around my area by flipping stones and walking into my kitchen!
Also if anyone wants pictures of bigheaded ants they are Pheidole species.
Just have the frogs let you know if they like them or not. I just drop a single ant in the tank and see what the frogs do. You will know right away if the frogs don't like that kind of ant, as they will scrape it off their tongue and not try to eat it again. Just be sure to remove any ants that the frogs won't eat.