There are many guys on this forum that will chime in with their experience.
So you know, corbeau sells seat rails that will bolt right into a miata. I had a corbeau forza with the driver's side rail. (jeff_man now has it) I just recently bought a sparco sprint from drift devil. I purchased a passenger side corbeau seat bracket and then modified it to fit the sparco seat. Now the seat just bolts in.
As far as side mount brackets go, memoryfab makes a set. I have a memoryfab seat with the driver's side slider as my track seat.