Try it without Battlemania turned on. I was having no luck until I switched it off, and then I started finding Chocobos every 3-4 fights --- I think I know, I don't think I know. I don't think I know that I know. I think I know even though I don't think I know. I don't think I think.
Victoly! After amassing 250k gil and CP that I didn't need, I captured a Black Chocobo. Spawned only six times after all that... Anyways, for those looking for help: try the ledge area, but don't jump off. Keep Battlemania turned off too.