A long tapered head bolt, a flanged nut, and a 2" section of appropriately sized fuel hose should do in a pinch. Put the fuel hose over the bolt, install the nut behind it, and begin to tighten until the fuel hose starts to distort and expand. Slide it in the end of the bar, and continue to tighten the bolt; the expanding fuel hose will keep the nut from slipping and will also tighten against the inside of the bar.
Suzuki OEM bar end weights are held on this way. It may not be as structurally intact as the pictured thingy for a barkbuster, but it'll work.
I may actually have a spare or two, let me look when I get home at 10:30.
Fuck Bill de Blasio