Don't be afraid of a cylinder bore gun if you find one you like. If you are interested in making the move to BP, then that makes me assume you are interested in the challenge. I made the switch last year. After a long search, a friend found an antique single barrel fowler in about 11ga. I was skeptical, but with use of shot cups and some time at the range testing recipes, I got a solid 20-25 yard turkey load. I had to hunt a little longer, but the extra time in the woods was well worth it. When I reflected on the birds I killed with my "modern" gun, many of them were under 20 yards. I killed both my birds last year with the ol' antique (affectionately named The Tube) at under 20 paces. It was a very satisfying endeavor.
Recently, I was lucky enough to find a T/C New Englander 12ga. It's an open choke gun (I've heard there are some New Enganders with screw-ins). I haven't had a chance to try it out yet, but I expect it is a great choice if you can find one.
Very best of luck to you in yous move to BP turkey hunting. I know you'll really enjoy the switch!