Imemsa seems to be the main manufacturer of pangas in Mexico. see http://imemsa.com.mx/
There are several dealers in Nayarit state.
There is also a manufacturer or line of Mexican pangas called Argos. The Imemsa dealer in Chetumal (Quintana Roo) sells Argos. He quoted me a new 12foot Argos panga, 9.9 horse Yamaha 2 stroke and galvanized trailer for about $50,000 pesos. I have not been able to find a manufacturer's website, but see http://nautimex.com/index.php?option=com_content&view=article&id=22&Itemid=34
I also am looking for a Mexican panga, either in the Ensenada area or Hermosillo. My interest is flats flyfishing. I live in Albuquerque but would use the boat primarily in San Diego, CA south bay (they have bonefish in San Diego!) but would also trailer the boat to Quintana Roo, paradise on earth.
Let me know what you find or if I can be of any assistance.