Marine, I've gone the same route as you are considering, with a 21 Trap for serious sporting clays shooting. So I know how you feel looking for a reasonably priced 21, 32" or even 30". They are few and far between. But they are out there. One thought, by the time you find a cheaper one that may need mech work and restocking, you might be better served finding a decent one that is good to go and has stock dims close to what you need to shoot well. If the stock is short you can have a spacer and new pad installed for sporting, keep the original pad in case you want to sell the gun later on. Not all that much additional cost. 21 Trap guns are usually found with a wider range of stock dims than 21 Ducks which generally have a lower comb. Personally I wouldn't worry one wit about modifying an all original gun, once you buy it it's your gun to do with what you will. 21's aren't all that rare. Also it's more fun IMO to shoot often and well with the gun than to keep it in a safe because it's mainly a collector piece. Again, everyone, that is just my opinion.
Thank you for your contribution to our country and the people of Iraq. I agree 100% with your mantra. Silvers
