Hey there, there is one shop http://www.marinasilcer.com
but they are quite informal, and much more focused on windsurfing and sailing. Riding in front of their club is not a very good idea, there is very little beach, and some wood pilings around.
There are another two dealers, one i distribute to, http://www.adventuretours.com.mx
, he is a master cave diver as well if you want to go diving in caves. I will PM you his contact information. Most guys ride in front of their beach houses, or get organized to ride at one person's house. As you may know the wind is just as good anywhere along the 150 km coast i have been around, so it's just a matter of driving around and finding an open beach. I will PM you Tony's email, he is an american living in Merida for a couple of years, great guy, great rider too. Yo can ride with those guys, really nice guys. How long are you staying?