One thing to bear in mind: if you get a SCSI2SD v5.x, the configuration is stored on the SCSI2SD itself, not on the card, so you'd need to have two cards the same size and use the same partition size. On the SCSI2SD v6, the configuration is stored on the SD card, so that would make it easier.
The cables are scarce, but the connectors themselves seem reasonably obtainable. The connectors in the faceplates I just got from RS's "own brand", and I got a few cables made up by a company who do custom audio and data cables, and the male connectors were part of their standard supplier's range too, so I'm guessing someone somewhere must still be using them for something? Interestingly, RS sell cable assemblies with a 3-pin mini-DIN on one end and bare wires on the other, but not a straight-through cable. So who knows. They aren't the locking connectors, just standard mini-DIN, but so far they seem to work (I haven't really tested them in anger yet).
It was moderately, but not unbearably expensive to get them made; no more so than it would be to get any other custom serial cable made, I suppose? I think they were about 15GBP each, maybe slightly more.
More of a "re-conquest" of sorts but I had to share as I'm pretty happy!
So some of you might recall when I picked up a huge lot of PowerBooks, including 7 2400s (technically 6 complete units (1 Mighty Cat and 1 boxed Japanese 2400c/180) and 1 fully disassembled one), for a pretty great deal. I sold one of the working ones to @jonpurdy recently and now with the stay-at-home order finally got a chance to look at one of the dead ones (GLOD when reset button was pressed).
It wound up having a bad CPU - I put in the spare G3 that I got in the same bulk deal and it booted right up. Unfortunately I do get an occasional cache error on startup but it's worked awesome so far. Plus as a bonus this 2400c already had a 120 GB Seagate HD installed along with a 64MB module, as well as a few neat extras in the bag it came with.
Now, I just have two more dead 2400cs to go... if anybody has a spare stock CPU for sale I would be grateful!