Well, then, that's a hard one, because they aren't approved for sale in the U.S.
Sorry I don't have more info at my fingertips, but I recommend you look in our
Skyline forum for threads about importing cars. You'll get the basics about procedure and cost. MotoRex is the main company importing Skylines, but they don't do Silvias... yet.
Keep your fingers crossed.
But, somewhere in one of those threads is the name of another importing company. I'd suggest digging it up and e-mailing them...