I always thought that Convict Cichlid fry would make the best feeders. You can get mature parents all the time at practically any LFS, usually from people trading them in (not knowing that they get mean when they have babies to protect). It's really easy to tell the males from the females - which is necessary for breeding fish (der). Most importantly, they'll breed in anything; 10 gallon tanks, cups of coffee, you name it. They're the little grey and black striped bunnies of the freshwater aquarium hobby. They can breed more than a lot of live-bearers, and that's really saying something.
I've kept a lot of fish, from guppies to frontosa and none of them have been better parents than the female Convict I had. They have huge, frequent spawns and they're very aggressive protectors - which means you'll have more fry to feed to your fish once you net them and grow out the fry.
If you have a few extra tanks to grow fry out in, they could possibly be a better alternative to guppies. Although, if you have trouble feeding guppy babies to your monsters, you should just forget about feeding them convict cichlid fry. Convict Cichlid fry are atleast five times cuter than guppy fry.