Remember that "red-tail boa" does not really mean anything, without geographic information with it.
Many pet stores call boas "red tail boas" to try to increase the value. Pretty much all boa constrictors have a reddish colored tail.
If you do not have a specific locality in mind, then you can buy a Columbian boa constrictor, (sometimes called the Columbian red-tail boa, but there is no difference) They are the most common and usually the most resonably priced.
If you want something specific ...then you look for (for example) "Peruvian Red-Tail boa", "Guyanan Red-tail boa", etc.
These animals may be very nicely colored (some are greyish or silverish or very light beige with a red tail)...but tend to be much more expensive.
You may want to do a google image search and get an idea of what you are looking for. There should certainly be some captive born boa constrictor babies at the all Ohio show.
Good luck