I can't say I have ever seen captive bred coachwhips or racers for sale. I usually let them go after a few weeks, or by the end of summer.
Glades herp Farm (Gherp.com) Sells black racers on occasion. For just 5 bucks. Only downside, they are super fast and super agressive (for the most part.) If you wanted one, just contact them and ask them to bring some to the next show near you (Im sure they will go if it's a large scale show.) That's how I got my trio, when I kept them.
Due to their fast metabolism, speed, and typical aggression, I can't think of many people that would have them as pets. Most species, anyhow.