They look really neat.
Spares are essentially non-existant. I managed to find a set of NOS pads when I had mine, but for piston seals had to source some EPDM X-rings. If I recall the flat head bolts for the discs are 5/16-22 tpi allens. Took me months to find replacements for them.
It was almost as good as the stock single Norton disc. Had it on my cafe racer for many years, but sold it to finance building a new Brembo sytem that really does stop!