All of the patents on the original NES have expired, worldwide. It is now 100% legal to clone an NES. The *ROMs*, however, still fall under copyright. But making a piece of hardware that can play NES games is perfectly legal now. (I remember reading about the patents expiring recently, in '07 or '08, IIRC. I know they expired in some countries before others as well, so NES clones became legal some places before others.)

edit: Indeed, here is one that is for sale throughout the US: Generation NEX. I've seen it at multiple local game shops.