Sorry I can't help with a lead on a shop that can help with your chamber. I am glad that you posted though. I am going to pick up a 6" barrel for woods carry. The WFNGC is what I like to carry. I have been debating getting a plain ol' Glock hunting barrel vs. a KKM or LW. You might have settled it for me. The Beartooth-style bullet feeds great in my stock 4.6" chamber @ 1.26", so I imagine that the Glock chamber might be more suitable for that bullet profile.
Again, sorry to not have a lead for you on fixing your KKM. They have a pretty good reputation so I am surprised that they are not making it right for you.