Even now the only way for one to obtain Renner or yeast is to purchase it. There is no east home recipe for these, so where did the ancient bakers get yeast and cheese makers rennet? This might include any other ingredient they obtained through outdated ways (not export/import).
now the only way for one to obtain Renner or yeast is to purchase it
Neither one of these is true. Rennet occurs naturally as an enzyme in the stomachs of ruminants, which is how ancient people got the stuff--Pliny discusses the differences in using the rennet from different animals. Yeast occurs naturally in the wild, although wild yeast is rather unpredictable. Brewers still capture wild yeast, intentionally or unintentionally, and make cultures of the stuff. Captured cultures of wild yeast are the origin of all commercial yeast strains, which were bred from wild yeasts