The Rainbow Venix disks were feared lost forever. I've managed to read them all and am processing them into the proper image files right now. It was the only true Unix than ran on the Rainbow, and should make a nice addition to MESS'. There's indications there might be source on these, but I think that's just a re-used label. There is a c compiler, so reconstructing sources may not be outside the realm of the possible, at least for some items.
My venerable Rainbow, though, is showing signs of failure. It flakes out after it's been powered on for a few hours. Still trying to figure out why and what my next course of action should be.