You might want to try Alan House near Bucklebury, Reading. I know he has many Piston Provost bits.
Don’t know what the situation is here because as well as owning the flyable one XF597 (G-BKFW) he was also restoring XF836 (G-AWRY).
This restoration has been on going for many years.
He did also have a couple of ex Irish air corps hulks lying around.