What about the Luxor? Have yet to see one.
You can always find one parked beside a Shamal at Los Santos International Airport (southeastern part I think). However, to get the plane without attracting police attention, you have to buy a hangar there (either as Michael or Franklin). This is the only spawn point for Luxor in singleplayer as far as I know.
@ReRuss I thought it was cut from the game. I wonder if the stuff it sprays will affect people like in the first trailer.