I found it on Xianyu, and it was dirt cheap. The seller even included some other stems.

That being said, there wasn't any brand mentioned on the Xianyu listing. Some people did mention that they might be "LCET" stems, but I can't confirm that myself.

I did find something similar on AliExpress once, but I don't know if they're the same.

In any case, they're pretty decent stems imo. They're pretty smooth, and very satisfying to use. Only downside being that they have more wobble than usual.

Overall, a pretty awesome upgrade over stock brown stems, and they sound great in Cherry housings too!