Go get one from a junkyard and try it...many times you can unbolt the seat from the seat rails and this would allow you to use the rav4 rails on many different seats...probably would require some fabrication work...
What system said -- haven't tried to change seats in the RAV, but my El Camino had several seats from a variety of other GM cars and trucks. All the seats bolted to the El Camino seat rails.