Hi Martin
If you Google the following words:
epoxy bearing materials and method
You will find a few posts I made for an epoxy bearing material process I developed in 2011. There is a PowerPoint presentation attached to them showing the process.
It used Araldite (The slow cure version not the 5 minute) to cast a nut. It is available worldwide. I also used the material to re-bed my lathe saddle after the ways were reground. I still use the lathe and there has been minimal wear since rebidding it.
The material is easily turned. one method might be to after applying a liberal amount of release agent to the splines of your tool thickly coating the spline shaft then allowing it to set. After it has hardened for say 2 days turn the coating to an even diameter and tidy up the ends (without touching the splines!) and press it off. To make a nice job of your tool maybe you could replace the brass bearing with one counter bored from the inside so that the epoxy nut is unseen. You could epoxy the turned down cast nut into the brass section.
The epoxy coat has almost no shrinkage, maybe coating the splines with a liberal coat of shellac before you apply a release agent would be a good idea. It will provide some clearance once the shellac has been removed with methylated spirit later. Otherwise the cast nut will be a very tight fit. I still have the test nut I did in the presentation. It has never worked loose. It also has a metal sleeve.
The design uses metal powder. Recently I had to turn some hard brass rod down. the brass turnings came off as very fine flakes. I kept them! While a bit coarser than the metal powder I suspect they might work for your application. You could experiment.
Regards
John