If you're looking for a Voodoo, I don't think you're going to find one in the city. Go out to Sandy Shores.
Yup, found one up there last night, driving from the Lost trailer park towards Trevors double wide, just on the outskirts of Sandy Shores (btw, I was driving a Rebel when it spawned). I couldn't keep it yet, because my garage is full with expensive cars... but I did drive it around for one GTA day. It was alot of fun to drive, a real floaty/cushiony ride... kind of like it would be in real life.