to be honest i dont know any in manhattan that would have any snes games. then again i dont go to too many hobby stores where they would have them, and the ones i've been in never have video games.
i've seen a few places in the bronx, brookly and queens that sometimes have a couple of snes games, as well as n64 (probably ps1, i dont bother looking) but none in manhattan. Your best bet would be to stop by any of those really small electronic stores that have a ton of sh*t in their windows and have no walking space.. the ones that just have one reeeeeeeeeeeeeeally long displace case and a ton of stuff on the well. thats the type of place that usually has older used games, so try your luck at that. Also, avoid any of those stores that are in or close to the big tourist hot spots since they most likely WONT have old games (old there would be ps2 and gc).
good luck!