I've found diamond abrasive segments available from a company in China. They're brazed to tools, like cup wheels. I want my bits to be reusable, so I don't think I would want to braze them on. From what I've read brazing is a permanent process, but soldering is weaker than the base metals and recyclable.

I haven't contacted the company yet, but hope they have something that will work and will sell, or give, small quantities for me to test. I'll also search a little to see if I can find the segments in the US first, since it would be easier for me to communicate with them.