Try Insite Arms in Lloydminster Alberta
If there is an action attached most "machine" shops are not licensed to work on firearms...
You could probably thread the 1/2x28 thread on top of the left hand threads. You would not have to remove all of the thread. It would look ratty but most likely would work just fine.
Like an old toolpush I knew once said, "a crossed threads a tight thread".![]()