See this long list of baking supply stores - ten years old now, but most of these will still be around: DIY baking supply / supplies - #47 by Dragonbones
The baking supply stores are weird places. The one near me looks like … nothing. Just a store front with plastic containers for sale. But in the back there’s flours and cake mixes and freezers full of nuts and who knows what else. I walked by it for years before I knew what it was.
Carrefour usually will have yeast too. In Taiwan I’ve always bought the little packages @Shaun008 just posted. There are other kinds of yeast available at the baking stores (probably not at Carrefour), but I’ve never gone far enough into baking to figure those out.