The same places you would buy any AP (guest relations). I like to go to the DTD location, mostly because it is a more leisurely transaction. Just take a picture ID and your DVC membership card (either temp or blue). We have done this about 3 times. I actually took the front sheet of my contract the first time since we were purchasing our grandson's AP and his name is different from ours, but his mommy is an owner on our deed (plus needed is correct address and that was listed on the deed). No problems, but they will and do ask for both forms of ID (picture and DVC).
We arrived to WDW late in the evening and also used the DTD location. It was so easy...no line and we were able to top it off with a yummy ice cream sundae @ the Ghiradelli Fountain!
We arrived to WDW late in the evening and also used the DTD location. It was so easy...no line and we were able to top it off with a yummy ice cream sundae @ the Ghiradelli Fountain!