1/250,000 scale topographic maps of Mexico are available from Tamassee.com. Three maps(size 3' by 2' each)cover the coastal area from Huatulco to northwest of Puerto Escondido and inland to north of Oaxaca City. The maps are about $10.00 each.
Mexican government map name and # Tamassee.com order #
Oaxaca E14-9 TMMX3117
Zaachila E14-12 TMMX3158
Puerto Escondido D14-3 TMMX3126
Another online map source is Omni Resources. The way they index their map selection is easier to use than the Tamassee.com site.