If you need more and can't figure out where to get them from, you might try using a standard carriage bolt. You may need to flatten the dome on the head a little to get it to fit, but the square part should keep it from rotating.
I was in a Big R store yesterday and saw bolts that looked somewhat similar, and were called "elevator bolts". They still have the square of the carriage bolt, but with a flat round head instead of the dome. The head was fairly large diameter, so you'd have to grind opposite sides down to get them to fit in the track, but either one might be easy to make work.
Chris