Neither Mexico or Puerto Rico are as simple as mailing a plant...at least not legally. Puerto Rico regulations are quite clear on the matter:
<<All plants and/or vegetative propagating material introduced into Puerto Rico must be free from sand, soil, earth, and other foreign matter and must be accompanied by an inspection certificate issued by the governmental authorities in charge of enforcing plant quarantine regulations in the state, territory or district in the U.S. from which the material comes. The certificate must bear the name of the state, territory, district or country where the material was cultivated; the name and address of the consignee and importer; and the accepted common name or scientific name of the plant. It must also indicate that the material was duly inspected and is apparently free of plant pests. The material must meet all applicable federal quarantines.>>
In short, you need a phytosanitary certificate from the state of origin to send plants to Puerto Rico. The cost of a state phyto varies from state to state.
Mexico is more complicated. For there you need a federal phytosanitary certificate and over and above that, you must treat the plants for two specific pests; though for the life of me I can't remember at the moment what they are. They need to be sent to specific cities that act as ports of entry...I use Merida and Mexico City. The federal phyto costs $50.00, plus a mileage fee for the inspector to come to the nursery.
Puerto Rico has an extensive list of prohibited plants which are not allowed entry...pretty much everything but lilies.<g> In contrast, Mexico has a list of plants that are approved for import into the country and it is a short list...very short and very few lilies are permitted.
Your best option is to find someone in Mexico that sells lilies. I can contact my customer, but I am leaving soon on a trip and won't be able to contact him until next week.