There are a number of places to find maps and it is advisable to purchase a site map for every ruin site you can, even if you are not even in the area. Think ahead, the map you see may not be available anywhere near that particular ruin site and you may visit it someday. Besides most of these maps cost less than $3.00.
Venues that sell maps are:
Chichen Itza ruin's store
Coba ruin's store
Uxmal ruin's site store
Dzibilchaltun ruin's site store
Xel Ha water park store
Xcaret store
Many all-inclusive resort stores also carry some maps.
The odd store in Playa del Carmen or Cancun will have some maps.
Libreria Dante Peon is an excellent bookstore in Merida that carries the entire "Dante" line of maps. This bookstore also carries lots of English and Spanish books on the Maya. It is located at Calles 57 at 60 in the Teatro Peon Contreras.
OTHER SOURCES
National Geographic magazines often carry an excellent site map of a ruin site they are featuring. You can either dig through your own collection if you have them or visit a used magazine store that deals in National Geographic.
Books - There are numerous books published regarding many ruin sites both large and small. Many of these books contain detailed site maps.
Magazines - Some magazines like MundoMaya offer site maps from time to time. Some travel magazines do as well although you would have to search through many to find something.
Bring light ponchos for rain gear. These can be purchased from most camping stores. Many stadiums also carry a light poncho to sell to fans of local football teams. These work great as well. They are small and light and easy to carry anywhere you go as a rain cloud can come in no time and dump a monsoon on your head.
The Mexican name for the Atlantic coastal region of the Yucatan Peninsula is Riviera Maya. The English use is either Maya Riviera or Mayan Riviera. It is used all three ways in this web site.