We do machine these screws ourselves - you can’t find them anywhere else.I'm using titanium screws to mount my cartridge(s) for a while. You can find them quite easily as Grade 2 (pure Titanium, medium solidity) or Grade 5 (alloy Ti6AI4V, high solidity) products. Experimenting with a torque-limiting wrench.
Much more difficult to get is Grade 4 (pure Titanium, highest solidity, seems to be available for medical application only). But I never found ready to use products (i.g. screws) of Timet 1100 (alloy Ti-6Al-2.7Sn-4Zr-0.4Mo-0.45Si, better solidity than Grade 5). At eBay, for instance, you can buy pre-product stuff only. Thus, in my experience, I take the quoted statement above as true.
@halcro - Have you ever considered to use the Arché headshell with your beloved FR-66s and the Palladian (or any of your other cartridges, of course)?