You might try Safariland or Bianchi. They tend to build holsters with retention straps. I carry a Kimber Pro Raptor in either a Crossbreed Supertuck or a D.M. Bullard Dual Carry. The only time that I have ever had a problem with a thumb safety being disengaged was with a Combat Commander that had an ambi safety. I didn't think that it was too big a deal considering the multiple safeties, however, I replaced the ambi with a right handed safety on both the Commander and the Raptor and have never had it happen again. I believe that with a well made IWB holster it is almost impossible to accidentally bump a non ambi safety off.