Powerhouse Automotive (UK) Ltd.
Supplied a service kit for front and rear calipers for my 1990 VX800.
Everything fits and the replacement pistons are beautiful stainless steel (unlike the seized, chromed and pitted originals).
About £120
Two day delivery to my chosen click and collect.
I found them on Ebay but you can deal direct with them.
They are a UK company based in Chesterfield.