first of all, very nice page. :)
There is a recent guidebook in Spanish which I deem the most complete available: "Guía de las altas montañas de México y una de Guatemala", by Jorge Neyra Jáuregui. It encompasses every Mexican mountain higher than 4000 m, as well as Ajusco and Tajumulco.
The book was self-published in collaboration with CONABIO. You can buy it in outdoor shops in Mexico, and the author also sells it through Facebook. Hit him up and also ask him for his "practical guides", a series of leaflets for field use.