An successful field trial dog that ran under AKC SPO (small pack option) rules are gun dogs bread to run cotton tails. A.H.R.A and UKC hounds are also good gun dogs.
On the other hand, AKC hounds that compete under brace rules are to slow for most hunters. The brace hounds are what give the field trials a bad name for hunting and because of such poor hunting ability the modern gun dog movement was born. This isn't to say that you can't get a bad registered gun dog bread hound because you can, just like you can buy a bad used or new car. Quite honestly you'll go through several hounds in order to get a good one, and the great ones are fewer and much harder to get.
Hound ability is genetic. There's a little training but for the most part they either have it or they don't.
If you want a good hound I suggest you learn a little about the hounds blood line, which is something you can't do without registration unless you have bread the blood for at least the closest 3 generations.
If you know what makes a good hound you'll probably be ok. If you don't I suggest you get with one of your local beagle clubs.
I was going to suggest a few breaders, but they only bread those inferior field trial hounds that seldom loose rabbits and can run the same rabbit for hours with a loss.
Again, just like any thing else, if you don't know what your looking for, be it a used car or a hound, then there is always a chance someone will sell you what you don't want.
Everyone expects to buy a field champion for $25 dollars.............
I hope you find one.