You can play and experiment . playing is fun.
True traditional ginger beer is made with a symbiotic culture of yeast and bacteria - probably mainly the yeast Saccharomyces florentinus (formerly Saccharomyces pyriformis) and the bacterium Lactobacillus hilgardii but maybe a few other minor variants thrown in as cultures like this tend to evolve & localise despite claims of purity .
However some people like the taste of ginger beer made with saccharomyces c. variations like brewers wine cide or bakers yeasts , using more usual brewing, wine/cider making methods
other make it with "water kefire"
or you can make ginger flavoured malt beer - or ginger wines ! Why not play and experiment a bit.
If going the more traditional way and you can't get a culture - why not try and grow a starter. (Ginger Beer plant) Dissolve some sugar in boiling water then cool it - feed daily or twice daily with grated ginger root (organic probably better for the starter as you want he natural yeast bacteria bloom on it ) and light sugar syrup (using clean vessels and covering with muslim. You'll probably find you grow a good culture - but if it isn't discard and try again.
Its a bit like making your own sour dough starter for breadmaking - you use the natural organisms then natural selection by discaring any off batches !
Have fun!