GMAT Testing Sights

The GMAT site has a link to find a testing center, and the closest one to STX is STT:

http://www.lmgtfy.com/?q=GMAT+testing+center&l=1

Test Center Information
Test Center: Pearson Professional Centers-St. Thomas VI
Address: Nisky Center
Suite 730, East Wing
St Thomas 00802
Telephone: 340-776-4910
Directions: From the airport, turn right on Highway 30. Go about .25 miles east to the third stoplight. The building is on the right. Look for the Nisky Center retail/office complex.

Testing site is located on the second floor of the east wing of the center (corner of the building closest to the intersection) - go in door above the Navy and Air Force offices.