I trawled through 7 pages on Ebay early this morning, searching "Compur", and another 3 for "Prontor", the 90mm f.8 Angulon also came in a Prontor but are rare. I tend to do a search about once a week and it has paid off, I've found a few brand new "old" shutters.
Wanted adverts are another way of finding shutters the US LF forum or Photrio (APUG) but you need to be a subscriber.
The early post WWII 90mm f6.8 Angulons have a reputation for hit & miss performance, the late Dean Jones (Razzledog) an Australian camera repairer used to make 5x4 Polaroid conversions and fit them. He discovered that the shutters themselves sometime had barrel lengths that were slightly out of tolerance affecting the spacing, he'd strip the shutter and machine to the correct tolerance, that corrected the poor sharpness some suffered from.
Linhof actually took batches of lenses from manufacturers and selected the ones they wanted after optical testing, returning the rest. The issue is supposed to have been resolved by the 5 million and higher SNs.
Sometime you can find the 89mm f6.3 Wray WA in a Compur, they are poor optically so often cheap, the cells would be a direct swap and the aperture scales match, The engraved FL is usually nominal anyway and the actual FL is often slightly longer and in a few cases shorter, and even then can vary +/- 1% according to a Schneider data sheet, I'm looking at.
Ian