Hi Scagda,
I bought my Polski Fiat on BringaTrailer.com from a gentleman in New Jersey. He had imported it into the US, but I don't really know the details. If you're interested and you live in Mt View, (near me in Palo Alto), you should come by and look at the paperwork he generated. My issue in getting it registered in California was that the DMV wanted me to get it smogged before they could proceed to register it even though regulations said that as a 2 cylinder motor it was not required to get a smog test. That's when I went to a remote DMV office and got it through... Let me know if I can help in any way.
-Chuck