I find ebay being overpriced if you are into collecting stuff so flea markets can be an option if you don't want to overpay.
I enjoy seeing glimpse into other people's niche hobbies.
I really enjoy markets like they describe and I've experienced them in Asia, but I have no idea where I'd find one in WA State.
This niche hobby became https://bernalcutlery.com/ which is a fairly successful Bay Area knife store