By your description I'm assuming you're talking about the "V" piece that would touch the tree. If you can't get them from the manufacturer, it would be real simple to make your own. From most any hardware you can get a 6ft x 1in length of steel you could cut them from($10). Drill the hole you need, bend to the shape you need with a vise, and bolt them on. I would say that you could probably use the lacking sections between good sections, but they are meant to be there for a reason. Any fall can be life threatening. How much do you value your life. Is it worth $10 and a little work? Just food for thought.
I worked for a hunting outfitter for 16 years and have hung thousands of climbing sticks of all brands and makes.