I'm no guru but I'll give it a shot....
I assume you meant how many subspecies of Drys. There is only one species that I'm aware of (unless caudomaculatus is a different species)
The ones that I'm aware of are:
- Eastern Indigo (Drymarchon corais couperi)
- Texas Indigo (Drymarchon corais erebennus)
- Black Tail Cribo (Drymarchon corais melanurus)
- Unicolor Cribo (Drymarchon corais unicolor)
- Yellowtail Cribo (Drymarchon corais corais)
- Mexican Red Tail Cribo (Drymarchon corais rubidus)
- Margarita Island Cribo (Drymarchon corais margaritae)
- Drymarchon corais orizabensis
- Drymarchon caudomaculatus
While none of them are bred in captivity in large numbers....couperi, erebennus, melanurus, unicolor and corais are bred in captivity with some consistency by dedicated breeders. I cant tell you how many of each subspecies are currently being kept in captivity but they are obtainable if look hard enough. Some times it requires getting on a breeder's list in advance. There is a very small number of keepers that are working with rubidus but they are extremely uncommon in the pet trade.
Chris