I want to start an ebay store, where can I find a supplier?

I want to start a small unofficial business on ebay to make a some cash for college. I was thinking of selling electronics and video games, but I don’t know how to find a supplier. Anyone know how this is done? Also, if I am under 18, would there be any legal things I have to take care of? I’ve been selling on ebay for about 5 years now, but just stuff I get at garage sales and whatnot, making a couple hundred bucks per year.So I know how to sell on ebay, but I don’t know where I can get items in bulk.