I don't think they made one specially for Pro-Stop fittings.
The RS-1s that ran Hope has a different machined linkage to the Pro-Stop, particularly since the discs were such different sizes:
Not so easy with the San Andreas, since you haven't got the linkage to adapt.
Maybe some sort of adapter like the ones for AMP to ISO, or on the Whyte PRST1?
Cheers! I did have an adaptor once, moved house, lost it! And they are more rare than rocking horse poo now. May have to go with a pimp set of rim brakes for the back but Hope disc front.