In case you want maps after all (never let someone else tell you you don't need them), Map Link, Inc. worked two years ago. I assume they're still in business.
Number: 1 800 962 1394
I think they're located out of Texas.
Maps are 1:50,000 scale. Can order color or B&W depending on availability. Availability might be low--especially for volcano related ones--as they are sent from the Mexican government.
Also, if you request it, they can probably fax you an index of all their topographic maps of Mexico. It's about 11 pages with about 100 map references per page. So, as you can see, there are a lot of maps. But then, Mexico is a big country.
Maps needed for certain peaks (depending on where you're going):
ORIZABA
Coscomatepec MEX50 E14 B46 (SW corner)
Salvador El Seco MEX50 E14 B45 (Tlachichuca locale)
Cuidad Serdan MEX50 E14 B55 (south approaches)
Orizaba MEX50 E14 B56 (south approaches)
LA MALINCHE
Tlaxcala MEX50 E14 B33 (NW of mtn)
Puebla MEX50 E14 B43 (SW of mtn; mtn is on this map)
IXTACCIHUATL
Huejotzingo MEX50 E14 B42 (mtn is on this map)
Back then, the cost was $10 each plus shipping and handling ($7.50?). Maps arrived in less than a week, but you'll want to leave yourself some extra time in case of mistakes (as in them sending the wrong map(s)).
----Paul