Rebuilding childhood collection from scratch?

Hi, GenX latchkey kid here, and my midlife crisis hobby looks like it will be trying to collect the sports cards and GPK that I loved as a teen and somehow misplaced over many moves.

Where are people getting vintage GPK other than just bidding on eBay?

Since I’m starting with zero cards, I’d love to figure out how to obtain more than 1 card at a time.