I email or call JNZ with a list of what I need. Josh has been really fast to get back to me with what he can get and send an invoice if I want to order it. Mitsubishi updated their system a while back and JNZ lost the ability to offer a full catalog on their website that we could browse, but he's still able to check inventory for almost anything across Mitsubishi dealers.
I've also used RTM Racing a lot over the last year, same situation, if its not listed, give them a call or shoot an email and they will check. The original owners/founders (Paul/Ziggy) of RTM had sold it for a few years to someone who didn't run the business well, so they are still rebuilding some of the inventory and catalog, but they are awesome people. When I reached out about modifying their STM sending unit to work with the GVR4 and not just the TEL, they were more than happy to make the change and I'm running one in my car now.
Only other place I'd mention is ExtremePSI, they've also been great for some parts and pieces here and there.