I don't know much about the USCF, but in Canada, our federation can calculate, with at least one rated player in the tournament, the rating performance and provisional ratings of all the rest of the unrated players.
To get a FIDE rating, a tournament has to be registered with FIDE, which has additional rules.
Might be best to contact the USCF directly:
http://www.uschess.org/component/option,com_wrapper/Itemid,327/
I am attempting to register my school for a chess tournament (NYC Mayor's Cup), but as my school has never had a chess club before, none of us are rated. I need to find out how to 1 register us with the USCF and 2 get us an FIDE rating. Any information would be greatly appreciated!