Welcome! There’s an active film photography community in Seattle between the photography discord and PCNW.
It’s not uncommon to see the 5x7 and 4x5 reducing backs on Ebay, but I’ve never seen just the 8x10 back and no camera. I wonder if your best bet might be to snag the first junker that comes by and clean up the back off of it.
Having my own meager darkroom makes me visit our local resources less, but I subscribe to both and keep a look out for events and workshops. I do see some adobe product "crash courses" in my future at PCNW.
I feel like I have seen various orphaned rear standards on eBay I never paid much attention to whether any was from a C1. I wonder if Blue Moon down in Portland has a graveyard of sorts?