Chris Hogg wrote:

If you didn't know anyone with a 'ginger beer plant' you could start
your own simply with yeast, sugar, water and ginger. I don't know if
it was brewers yeast or bakers yeast;

Apparently the 'true' ginger beer plant is not just yeast, but a
symbiotic mixture of a particular rare yeast and a bacteria ...

https://www.gingerbeerplant.net/about.html

You can buy starter kits there, though rather against the original
spirit of the GBP, you're not allowed to give it away.