The name of the beauty supply in Plaza Las Americas is called Beauty Factory. The store is located on the 2nd floor near Sears as it was mentioned.
I've seen some Dominican brands at Walgreens, including Silicon Mix and there is a chain of Beauty supplies called Sal's which carries Dominican products, too.
The Dominican section of Puerto Rico is called Santurce. It is a section of San Juan.
My cousin has been to a place in Santurce owned by Domincans and she calls it the Dominican product heaven. I will try to get you phone and/or address.
HTH. If anyone has any questions about Puerto Rico feel free to ask, hair related or anything.