You can get them anywhere that has a large body shop fastener section. My seat was warped from the sun. I used plastic carriage bolts and plastic wing nuts. All the holes are accessible from underneath and they held the seat tight when the clips wouldn’t.
Orchard supply. They had 1/4 plastic carriage bolts about 4 inches long. I cut them shorter and used plastic wing nuts. At least I think they were 1/4 it was a year ago. Could have been 5/16. Anyway they slipped in the holes in the seat and through the hull. Worked great.
