Most of the sets were probably used as postage and discarded, so it is likely that no more than 2,000-5,000 remain.
With a population of about 109 million, Mexico has a diverse and developing economy, but modernization remains a slow and uneven process. Current challenges include addressing income inequality, crime, corruption, upgrading the infrastructure, and reforming tax and labor laws. Annual GDP growth has averaged about 2% over the last five years, which takes into account a contraction of 6.5% in 2009 due to the global financial crisis. Stamps of Mexico are popular among collectors in the U.S. as well as in Mexico, and those who wish to learn more about Mexican stamps should consider joining the Mexico Elmhurst Philatelic Society International (M.E.P.S.I.). MEPSI provides many useful services for collectors of Mexico, including expertizing Mexican stamps.
"The Stamp Specialist" blog features buy prices for stamps which I am interested in purchasing. The buy list for Mexico includes the set recommended in this article. Viewing dealers' buy lists every now and then is an excellent way to keep current on the vagaries of the stamp market.