Bestop warranties lasts for two years. Are you still within that window?
If it's just the bolt, you wouldn't need to replace the entire clamp. I think
it's just a run of the mill machine bolt. You can probably run to a Home Depot and change it out. The installation instructions
note that the bolt is 5/16 x 1-1/4".
I have the same clamping system that you do. I'm trying to remember how it works. I only touch it twice a year.
Otherwise, Neil F. is right. According to Bestop's Support page
, you can buy replacement parts from them by contacting their customer service department. Again, according to the installation instructions
, it looks like the part number is 378.59.