This could be very difficult (and/or expensive) unless you moved here temporarily on a business assignment or have been posted here by the Italian government. Later Alfa Spiders were never sold in the United States and therefore do not conform to U.S. DOT and EPA regulations. The government has made it very difficult for an individual to import cars less than 25 years old. Expensive modifications may be required. If you and the car are here only temporarily many of these rules may be waived.
I would suggest doing both a BBoard search and an internet search on vehicle importation. There have been many postings about bringing in nonconforming cars on the BBoard and the government DOT web site has a comprehensive (and somewhat confusing) list of regulations and restrictions. That should get you started.