Depending upon how many tanks you want to dedicate to them I would look at something like this
3 different cryptoheros like marbled cons, HRP, cutteri. You could do any different 3, just continue to mix it up with your orders to try to get different types everytime
oscars
Green terrors
EBJD's
Severums
Chocolate cichlid
Geophagus Altifrons
Geophagus orangehead
Geophagus brasiliensis
Satanoperca leucosticta
2 different parachromis. Just keep mixing it up so you don't always have the same thing like the cryptoheros
2 different Herichthys at all times. Mix it up just like the others
2 different Vieja's at all time. Mix it up just like the others
1-2 different amphilophus at all times. Mix it up like the others.
I think this list would give you a great starting point and you would have a better group of CA/SA fish them pretty much all local fish stores. From this list you will be able to tell what sells and what doesn't pretty quickly and can mark them off the list if they don't work. I would buy them in smallish groups until you know you can sell them. If you keep your list mixed with the different groups you will keep people coming back. And of course throw in some rare ones every now and them like pikes, festea, less common fish, etc.
Good luck