Duo-R-
I'm still using that PSX adapter cable that came with the system. I need to replace it since mine is very flakey. All you would need to make one is a regular SCART cable, the correct DIN connector, and hook up the wires. I'm not exactly sure what to hook where, I forgot when the pinout is on our modded systems.
I emailed Chaoticjelly a while back and asked him if the RGB cables he makes for his own modded PCE's would work, and he said they should, he thinks the pinout is the same. I meant to order one from him but I never got around to emailing him back.