The hooker who comes from New Vegas is now in Fallout3 Let this hooker take out anyone who stands in your way. Weilding a scoped 44 magnum and some sleek Power Armor, this hooker is ready for anything. Also if you want Nissan in New Vegas check out the Nissan Companion Mod for New Vegas 
If you cannot find Nissan try looking in Megaton or area surrounding Megaton

1.1 Patch Notes
Fixes 2 Nissans Glitch