Wooziz pink Elegy and Fortuna you must get them in the main storyline
you can acces this races later BUT once the timer expires when CJ is out of his car he is spawn back to the race Icon in the city so AFAIK it's impossible to get them !!!!!! in storyline CJ stays there and gets "mission failure"
besides it's rather easy to get them in the storyline
and I think you should try to get both white and black Camper's from Jizzy they are easy and you have plenty of garages in San Fiero
the Truth Camper I got it without cheats in Black Project , the trick is to push it with Rhino in garage and block it from existing from the garage with Rhino before commiting suicide
and another small warning, with the SWAT tank in End of the LIne , don't push it into the Fortress !! because if you do it and go destroy it in garaje it will LOSE it's BP/EP abilities !!!
you must drive it to a grage straight away
another UCV which comes in small variation in the golden Burito in T-Bone Mendez, it's come seither with the small rear wing or not, personally I like it more with the wing, reminds of the A-team van