You can also try defrosted human consumption: Mussels, Clams, Prawns, Squid... then on the other side of things, you can also try breeding crays for them?
Then once you know what they will eat and won't eat, just start mix matching things to keep them interested in those foods...
BTW, how often and how much are you feeding them? coz maybe your feeding too often which is why they aren't showing much interest in their food?