Silverado Under Seat Subwoofer Where Can I Buy Subwoofer Boxes For A '97 Silverado Reg Cab?

Where can I buy subwoofer boxes for a '97 silverado reg cab? - silverado under seat subwoofer

I will go into the seat. I am not looking for 12 shots and only 8's. I think there is enough room for 4-6, but I did not pay $ 150 to build one for me. I do not want to see me when I leave 6'1 and my place slipped back.