It depends..
I find a lot of stuff at Flea Markets and Garage sales..mostly Vintage systems and games..

I buy all my new system games retail from stores like EB/Gamestop.

I buy stuff off Ebay that I can't find no where else like ...rarities/Neo Geo AES and MVS carts.
I always have at least 1 bid on some MVS cart auction at all times.