I would like some suggestions on a good anti friction additive to epoxy. I will replace my hobby mill's brass leadscrew nut with a 'cast in place' nut directly on the leadscrew. This is not a new idea. It is a very effective easy way to virtually eliminate backlash.
I've read that graphite powder is good but can be hard and therefore may cause wearing. Molybdenum is better but hard to find. Fine aluminium oxide can be good too.

Interested in info regarding additives, suggested epoxy/additive ratios and hopefully suppliers too!

I've used molybdenum disulphide powder/paste in high duty cycle applications, and found that it is a very effective abrasive.  I wouldn't use it on a leadscrew.

How about a split nut made of Teflon, with a pinch bolt?

Or a brass nut, and a brass locknut, locked together by an axial setscrew?

Or a brass housing like a plug valve body, filled with Teflon?  You can tap the Teflon if you like, or just leave a clearance hole.  Put a threaded plug in the open end, and use a big wrench on it to compress the Teflon.  It's amazing how much you can distort the stuff, plastically.

The aluminium oxide you mentioned is amazingly abrasive, Moh hardness of 9, in fact it is used to make abrasives.

You could add fine PTFE powder (as already mentioned) or add a fluoroepoxy that polymerises in. These must exist as I have seen them used for anti-graffiti paints. Adding some kind of silicone should also work. You can get the PTFE powder in an aerosol spray can from RS Components for example to try it out.

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