Now if you are talking about "socketed upgrades" for the SE/30 being ultra-rare, then yes, I've never seen one sold on EBAY in the last 5 years of looking. They must be out there though, most likely hidden inside an SE/30 which the EBAY seller is unwilling to open. Then the person buying it either doesn't know its there or they keep it secret. But I cannot believe that only a couple hundred of those socketed upgrades were ever made, which would explain why we never see them on EBAY. Certainly, they must be out there, somewhere!
They could easily have all been trashed. There were never all that many of them sold. A machine displays no external sign that one is present. A great many, probably a vast majority of SE/30s manufactured have been scrapped by now. It is possible that every SE/30 with one of those upgrades was scrapped at one time or another...
I have a similar worry regarding the "docking card" for the Outbound Laptop Model 125. As you may recall, Outbound's early business model required a purchaser to own a Mac Plus or SE. They then took the Plus or SE to an Outbound dealer who removed the ROMs and installed them in the Outbound Laptop. Then a docking card could be installed in the Plus or SE which allowed the Outbound to use the desktop machine's ports, memory and display when the two were connected by cable.
A Plus or SE with the docking card installed would appear as a broken machine (does not boot -- no ROM installed) and the only clue would be a little connector sticking out of the right side lower vent hole.
I really want one of those docking cards. I suspect they have all been scrapped as Pluses and SEs with them installed are discarded as non-working, their association with an Outbound Laptop long forgotten.