This came to mind as a possibility https://www.amazon.com/Daystar-Universal-Firewall-Accommodates-KU20040BK/dp/B004K2285E not the exact part you were looking for but very close and should work well.
Or try a search for rubber wire grommet with boot and a few other options will show up. I'll be following this project for sure!
Or try a search for rubber wire grommet with boot and a few other options will show up. I'll be following this project for sure!
