There are many vendor p5's, but most of them are located on the west coast. Therefore, they do not show at the east coast events. As far as competitor p5's I could not answer that for you.
Remember also, Mazda is supposed to be phasing out the P5, so that could also be why they are not having them at thier booths for shows. They only had a new black Mica MSP, and an RX-7 from a private competitor in thier booth.
They do not have any controll over privatly owned competitors, to make them come to the shows.