One of the shops is 2-blocks south of the Cathedral, Governor's Palace, & Plaza Tapatio. The other (larger) shop is located on the basement level of a shopping center called "Plaza Mexico". Stay thirsty my friend.
Hi, As promised, I'm posting what I found when I was in Mexico. I looked at a few coin shops in the centers of both Mexico City and Guadalajara, but most of what I saw there were cleaned and problem coins. You might get lucky and find something great, but I wouldn't count on it. The "real" coin shop in Mexico City that I found, where I purchased a Maximiliano peso, is called Numismática Plaza, located in the Plaza Universidad shopping mall (not in Oasis Coyoacán, which Google Maps erroneously shows). They have almost any Mexican coin you could think of, as well as a decent foreign selection. The "real" coin shop in Guadalajara that I went to is called Coins Briggs, and is located in the Plaza México shopping mall in Colonia Vallarta. They have a nice selection of Mexican as well as foreign coins. I hope this helps!