I had a very small batch of these made last year. They are for alloy head 650 engines (valves have the semi-circular annular stem groove) and were made from EN24T steel on a CNC Swiss lathe and are pretty accurate. I've been contemplating selling them on my Ebor Bikes website but the price would probably not be as cheap as old BSA stock, so I haven't listed them. I had been contemplating using them up on engines that I build. If anyone is interested they are wecome to PM me.
Cheers,
Jon