Tonneau cover replacement parts - help!

I've got a Leonard soft tonneau cover on the back of my Mazda B2500 pickup
truck, and the rear panel on the frame that is removable (the part that goes
over the tailgate, the rear snaps on the fake leather-grain canvas cover
snap into it) is now lost. I've been hunting around online for days looking
for a site that offers replacement parts but have been unsuccessful as of
yet. I don't want to spend between $200 and $400 for a new cover when all I
need is one plastic frame piece for a perfectly good tonneau cover.

Can anybody point me in the direction of a site or store that offers them?

Thanks!