I made 30+ of them, casting them in aluminum in sand molds. It's not an ideal method to manufacture them, and my scrap rate was high, and this reflected in my price.
After seeing them work in metal, Russ commissioned a die cast in China. The company was hard to work with and "lost" his tooling, and he didn't order any more.
I'm investigating what it would take to make a small die to cast them here myself. I have too many projects as it is, but making a die is something I've always wanted to do