Pretty sure you could find a lot of leather sandals made local there in shops or by street vendors. Mallorca especially has a lot of great shoe manufacturers. One that comes to mind is Carmina. They don't make sandals but they do have slippers. Are you looking for mens or women's sandals?
these are traditional spanish Espadrilles. I'd suggest something like this over sandals.
https://www.carminashoemaker.com/slippers-loafers-brown-suede-80384