You need to state which part(s) you need. Although I seriously doubt anyone is making ANY aftermarket parts for the top.
Before you jump to conclusions about which parts should be made of which material, realize that a very complex mechanism such as this top has many failure modes. Some parts, if they didn't break first in the event of a failure, may result in catastrophic failure of more important, and expensive, parts. It's possible someone goofed, but unless you have the complete project FMEA and are competent to analyze it, I wouldn't be quick to judge.