I found https://π.duncano.de which has an xcursor-theme inspired and based on the plan9 cursors set:
Installing that on my system, it turns out the Wayland ecosystem still has a hard time with cursor scaling. So I tried my hand at fixing the problem and making something that will be usable once more modern approaches take wider hold.
I have created SVGs based on the above pixel-based cursors and written a script, that is heavily inspired and based on what I found in KDE’s Breeze sources.
Check it out: https://git.sr.ht/~robertgzr/plan9-cursors
You can test the shapes of your installed cursor theme here.