For the physical release availability you need to contact the good people at K&A directly.
The game runs fine under VICE and C64 Mini.
Viewing post in Nixy and the Seeds of Doom (C64) comments
Ok thanks. I might just play the digital then which I don't have an issue with. I was mostly just interested in the physical but I noticed they are actually overseas which might be a problem with the tariffs.
I'll probably just design my own physical and burn it to a disc for my computer since I don't have a real C64.
Looks like a handful more are available now:
https://ka-plus.pl/en/store/Nixy-and-the-Seeds-of-Doom-C64-Cartridge-Digital-p72...