Thats not to say they wouldnt take bolivians, you never know. Theyre just already quite common. The next step for me would be to ask the shops if they would buy any kinds of dwarf cichlid off you, and narrow it down from there to ones you like too. I really think apistos would be fun!
Also other fish that you may have ruled out mentally but still might be a good option - eg, you say no livebearers (personally I don't blame you) but there are more unusual and uncommon ones around than just guppies and platys etc, so they could still be sellable.
I'd love to set up some breeding tanks as a hobby but I think I'd stop enjoying it if I couldnt move the fry on at all!