Other than the obvious… Facebook Marketplace, Craig’s List & Kijiji.
If you haven’t already, you may want to check out your local camera shop (if you have one).
…many will sell used equipment, know of people selling equipment or will have a “on the look out for/want to buy…” list
Local camera clubs are also a great source for used equipment.
You may also want to look at B&H Photo Video. I believe that they have/sell used equipment.
Sorry I couldn’t be more helpful.
