Then look for other smallish cichlids. None of the fish you listed are fit for a 20gl. Perhaps, kept singly, you could keep one but then you'd be missing out ont he social behavior these fish are so popular for.
If your petsmart ran out of keyholes you could wait till they got more. Petsmart also carries bolivian rams from time to time.
If you can't find anything there shop around. Have you visited any privately owned fish/petshops that carry smaller cichlids?