a simple google search brought up a few places online, although the one i chose to click on said out of stock. theres amazon. and dont forget garage sales. dont completly write off ebay. just find a store with very good feedback and uses paypal.
my little brother lucked out a couple of years ago. an elderly neighbor had bought an nes 20 years ago to give as a gift, but never did. it sat in her closet all that time until she told my brother about it and then she gave it to him. a brand new nes, still in box, never opened. he could have sold it for a modest amount...but he opened it and played it. cant say i blame him though. its harder and harder to find a working nes these days. i can get mine to work only about 25% of the time. fine for tetris, but forget final fantasy or dragon warrior.
hope you find one.