Searching for my US marriage certificate

I was a Japanese native and married my then husband who was serving in the US Air Force in March 1984.  I thought I went to the US Consulate in Tokyo for the marriage registration.  However I just discovered this was not the case. According to the US Embassy site, the US government does not officiate any marriages of an American citizen and a Japanese in Japan.  All the same I relocated permanently to the US and did obtain all the necessary US document through the marriage. I was naturalized in 1991 and I possess a US Passport, so the marriage should have been officialized somehow in the US. It's been over 30 years and I have long since lost contact with my ex-husband. I have no way to retrace my record.  How can I go about relocating the record?  I now live in Italy for over 10 years and I need to have some bureaucratic records in order in order to apply for the Italian citizenship. I would greatly appreciate your assistance!