A machine shop can do this as well or even yourself. All you would need is a bottom tap to fix your treads. If they are beyond repair you may need to go to a different style bead or retap bigger and install a heli coil.
Hope this helps.
"No man is smart, except by comparison to those who know less" ~ Edgar Watson Howe
Parris Island 2nd Bn F Co Plt 2114 11/15/91 "James Gang"