My friends brother is into the exact same thing. He has about, probably an entire shelf full of retro nintendo games and items. Probably about 500+. I'm sure I could find what you need, he has spares of games, sometimes like 5+ of the same one he would sell me. I also have access to flea markets around my area.
I live in Utah... We mormens have this thing with saving everything.. We send it to a GIANT thrift store. I find games all the time there. But I have never bought any since I dont play them.
Add me [email protected] if you want and I can keep a eye out what I find
Very easy; this is a good guide
But expand your knowledge && you can make thousands of dollars of profit; but this is more of a hobby. wont make you a steady cash flow.