Start with your custom barrel makers, OTT (On Target Technologies), Bullberry Custom, and Match Grade Machine. There's a barrel sale happening over on Specialty Pistols- one of the guys who works for them has short barrel lengths available in various twists. Then there's Gary Reeder (hope I got that right) that makes full customs. I might get censored here but, there's lots of people out there. EA Brown makes some 7mms that sound great.