I was talking to an old racer today in my LBS. Fingers crossed he can find a specialist who either stocks something or can make them for sensible money I will keep this thread updated for future reference. It would be a shame if they can be enjoyed properly when the parts wear out.
If they're largely cylindrical, you can get dimensions, and you have, or know someone who has, a lathe, you're golden. I've got a lathe
Offcuts of POM / Delrin are cheap. Likewise bronze, at least in the sizes you'd need for bikes. Oilite would probably be the best, but it's an arse to machine.
On the other hand, there's a metric (and imperial) ****load of standard sized oilite bushes, if you have dimensions, it might be worth souring the web for such. If you have to shave a bit off in terms of OD or length, it's easy enough to handle, the problems come with machining the bearing faces, where your tools have to be *super* sharp, and you can't really use reamers to get an ID dead nuts on.
Oilite's your friend if it's metal on metal, ebay search "OBFiiooll", where you replace ii by the ID in mm, oo by the OD in mm, and ll by the length in mm) so, f'rexample OBF101320 for a 20mm long bushing with a 10mm ID and a 13mm OD.
If you can't get the size you need, get the sliding interface dead nuts on, and then oversize the rest, it can be machined off to fit. So, let's say you need 10mm ID, 14mm OD and 18mm long, you'd probably want something like OBF101520
Coggers, please update this thread for the SAB MKII if you get the exact specs or alternative readily available supplies.