You could find it at the pet store pretty easily--it's a pretty standard product. Just look around a bit at some of the ingredients in the medications and you should find it pretty quickly--sometimes things with fancy names are really simple things, lol. Betta Revive has some methylene blue, but it also has neomycin, which is an antibiotic that your fish doesn't need nor should have, so stay away from that one or others that have antibiotic ingredients.
This is what mine looks like: http://www.fosterandsmithaquatics.co...fm?pcatid=4822
Keep in mind that this stuff stains like nobody's business--it would be best to get some kind of dropper to dispense it and be very careful about getting it on fabric or your skin. I spilled some on my hand the other day and I'm still blue.