Hey there Mickitlfk7,
Any dive shop with in the Metropolitan area should be able to help you out, specially if your going to be visiting the San Juan area near the beaches.
Most of the dive shops in the metropolitan area are pretty good and chances are they deal with NITROX in order to keep up with the competion.
If you desire any specific information feel free to contact me at:
Discovery70@hotmail.com
Good Luck and safe diving