Out of curiosity, is there a list somewhere with the non Priority Pass participating locations?
Not that I've seen. However, Plaza Premium has more than 80 lounges, and Priority Pass includes 60 of those. So about 20 must be out.
If you mean a list of *currently* accessible Plaza Premium lounges (using C1 card), here it is:
https://www.plazapremiumlounge.com/e...ges/capitalone
This is all of them, I believe.