Many of us know how annoyingly rare the proprietary IBM PS/2 SIMMs are.
IBM were far worse than Apple back in the 80's for making everything proprietary, and the PS/2 line became a meme for that.

Regular 30-pin parity SIMMs are common and relatively cheap.
I have a PS/2 Model 30-286.
This will only accept 9-chip SIMMs, and not the higher density 3-chip ones. Apparently the Model 50's also need 9-chip.

I had two 9-chip, 1MB SIMMs I wanted to try the following guide on:
http://john.ccac.rwth-aachen.de:8000/misc/ps2cache/

The guide is for 3-chip and 9-chip modules for an IBM Caching SCSI Controller which also used the proprietary SIMMs, but the guide also worked for my Model 30-286.

This picture shows what you need to do for the 9-chip ones.
CUT two traces.
Add four links.

I was lucky my SIMMs had all the traces that needed cutting, on the back of the module, as well as all the needed pins accessable through vias on the back, as the chips are very close together on 9-chip 30-pin SIMMs.
The modules I had success with were SIEMENS HYM91000S-70.