Like so many other vintage owners, I have a target 360 antenna with a worn out worm gear. My solution was to make my own with a 3D printer. I have posted a picture of the gear and the file that I made to create it (two files, the second has a really good support for the threads. I wish I could make these for everybody who wants one but I just don't have the time. So... you can either get a 3D printer and print one yourself or find somebody that likes to do these things. Personally, I'd say that it's worth having a 3D printer if you are into vintage anything.
Okay, so it won't let me upload the .stl (3D part) files, I will post them to thingiverse and add the link.
Target 360 worm gear by noslenwerdna - Thingiverse