Adrian said a few years ago that rams were getting very rare. If he hasn't got one, no-one will. You'll need to repair it or find a wreck. Ford D trucks(?) had the same set up but can't be used. The rams are shorter.
I have the work shop manual showing how to repair them. If you send me your email address, I forward you the scanned section.
The hardest part might be getting the special seals. Maybe try Adrian again to ask if he has the spool O rings and the piston seals. He might have them.
The actual repair is not complex. That's the beauty of Bedford buses.
It has a spool/valve inside it. When the steering wheel is moved, it opens the spool and the ram moves. It's important to get the right, otherwise the ram will drive to full lock, or "shudder" as the spool tries to find the bypass position and the driver tries to keep the bus straight. Bit like a 3 point linkage being out for adjustment.