Just as the title says... I've found several import sites but are there any that sell them pre-imported?
Not that I'm aware of. It wouldn't be cost-effective for any of them to front the international shipping costs for you. Plus, many sellers don't even have an American presence -- they have nowhere to ship them to in America other than to customers.
If you stick around forums (such as this one), you'll occasionally find people in America selling off carts, so you can save on the shipping there. Otherwise, just buy multiple games at once from Japanese sellers and you usually save on shipping.
Yeah I wouldn't make the mistake that I made when I first started collecting. I bought a bunch of individual games and lost my ass on shipping. Nothing like paying ems on 1 fds game...then when I got the game it was bad. But that was another story all together.
Famicom World!