These don't have to be fireproof like a firewall passthrough. They literally just have to block air and not melt in the 150-ish heat soak after shutdown.
Based on that, you can make them out of just about anything, even for the big hole required for aviation leads. Two pieces of .032 aluminum with U shaped channels scissored together with a grommet around the wire works fine. Heck, a plastic cutting board from the dollar store would probably work as well.
