Taco cart catering for a party
Without knowing where in NJ you're located, Taco Truck was my first thought; they make EXCELLENT tacos.
Another good one (def with a truck) would be Taqueria Autentica http://taqueriaautentica.com
Finally, if you're in central NJ, you might reach out to the owners of Mogo Tacos (on the boardwalk in Asbury Park); I don't know if they have a truck, though.
Let us know how you make out!