Most (not all) people in the hobby buy military trucks because you get as much truck as you can handle for a fraction of the money any civilian comparable would cost. While people like their trucks, many will eventually move on to the next more modern model that can be had cheaply, rather than spending endless money to keep their old truck shipshape.
Droves of people give up on the M35A2, as evidenced by the forum activity, and move to 900 series 5tons (cheap) or even FMTVs (not cheap). The right truck is decades younger and has lots of useful service live on especially the expensive components.
Communal users, such as fire departments, are also slowly transitioning away, substituting the M35A2 with trucks with automatic transmission (M35A3 and 900 series, the odd FMTV).
Yes, there will always be a hard core following for the Deuce, but whether this is enough to make a living, I do not know. Would I "like" truck parts precision made in the USA? You bet. I would be willing to pay more for them, within reason. There are still many M135 around and the torqueflite is notoriously problematic. Still, nobody makes even a new overhaul kit for it, let alone a new tranny. That's all I can really say.