Wandered over to those parts this weekend and while there isn't one next to the crazy cactus, there is one further up the street on Baselstrasse.
Either way, if anyone is looking for it, it's called El Sombrero Latino.
http://www.sombrerolatino.ch/home/home.html (the website is more impressive than the store itself!)
Not at all the selection you get at El Maiz, but served me well as I was just looking for Maseca corn flour in order to make corn tortillas. They also had a decent selection of canned goods (including tomatillos, black beans, nopales and chipotle peppers).