Have you looked near the seat tracks for any brand information or part numbers? If you have an inspection mirror, looking under the seat might yield helpful information.
Are they power adjust? What do the power controls look like? Some brands have a very distinct style to their controls.
Do you know approximately when these were installed? Do you know if they've ever been re-covered?
I'm leaning more toward a Chrysler or Dodge seat (300M, 300C, Intrepid).
-Rod