I found some threaded inserts at Menards in the hardware section (in the specialty drawers). They are not sized like the originals, but I was able to find a size that worked. If I remember correctly, I had to buy the screws that matched the insert (I don't remember if they were the same as the original equipment screw size/thread pitch).
I found that when installing the threaded inserts, to get a good hold I used some epoxy. But before using the epoxy, I used a dremel to put some good teeth inside the hole. Make some good grooves in the hole so that the epoxy actually mechanically locks the insert in the hole (rather than relying on gluing it in, the epoxy and key the insert in).
If I can find the ones I used when I get home (at work right now, working real hard) I'll take a pic and post up a reply.
- Frank
1984 200ES Big Red
1985 350X (x2)
1986 350X
1986 250SX
1984 Auto-X
1984 ATC70
1985 ATC70