Any good machinist should be able to thread the barrel and carbide should have no problem cutting the threads. If I still had my lathe I would do it for you...Machinists are like doctors...some are good and some I would not take my dog to. If it were me, I would look for a small shop that possibly had a CNC lathe...they could program a dummy part and get it dialed on that and then do your barrel. It would take the machine less than 30 seconds to thread it and do a perfect job...the time is in programing and set up but thats pretty fast with a skilled operator. The dummy plug would get the pitch diameter dialed in and you could try your supressor on it for a good fit. There are many small shops with capable people in them that could do a good job, it does not have to be a gun smith...many machinists have a lot more experience threading parts than a smith has. Check your yellow pages and look for a small shop...bigger shops do not want to bother with a nickle dime job and even $180 is nickle dime for them. Not sure but I think a 1/2-28 is what most supressors use...depending on caliber.....Another thought...just send it into S&W and have them do it for you...they probably charge less and may just do a barrel exchamge.....fed ex it next day air and it would be back quickly. Just my thoughjts.