If a belt pump can't be found, 97 and up C280 / E320 / SL320 used an electric motor pump that could be adapted. These were probably used on other models in that era as well. The clutch trigger wiring isn't strong enough so use that to trigger a relay coil. The contacts need to go to a 40 A fuse and the battery.

An alternate solution is to find a 99 ish S-10 Blazer or 99 ish Ford Taurus as they used an electric pump as well.