Highly Conductive Set/Grub Screws?

I picked up a Caravela clone that came with all three tubes, but only one default set/grub screw. Unfortunately the only batteries I have that will allow it to close seamlessly are some 350s. None of my 500s or 650s will close. Considering the only adjustment available on this thing is different size set/grub screws (510 power pins) I need to source some various sized ones.

I've looked around and all I'm finding are either stainless steel or brass with some kind of coating on it. Nothing just plain brass, or other good conducting metal. Does anyone know where to source these?

 

If this place doesn't have what you need, I dunno.
http://www.fastenal.com/web/home