what brand are the highway pegs?
I know these aren't Rivco, but I called Rivco a while back for 2 pieces for the mounting hardware for their pegs. I figured they would make me buy the wholle set of hardware for $149, but ended up telling me they'd ship those 2 individual pieces I wanted for $16...
So you might call the manufacturer, be real nice, and see what you can get done...
Also, out here in West Texas, we have lots of places that specialize in nuts and bolts... Oilfield needs 'em pretty often. They can get pretty much and size, shape, thread, head you can think of...