Just to clarify if you want the cornrow braids like the OP that can be done by appointment at any of the salons. IIRC, the Beach Club, CR, GF and Dolphin all have full service salons that will do cornrows with an appointment.
If you want the hair wrap with the colorful string and beads every resort has a stand at the pool, depending on the season maybe only during the weekend. All 4 parks have it as does the boardwalk in the evening. No appointment necessary but sometimes there is a wait.
Most recently I have been having my dd's cornrows done here at home just prior to a trip. They come out great, cost a little less and we don't "waste" vacation time. Just another idea ~~
TJ