Check with Balashi and maybe Heineken and maybe the reps for other beers on Aruba, like Polar beer is available at TEC Inc.
Kegs are also sold in the supermarkets, but they are these mini kegs. Some are easy to use, just cool and open, others require purchase of a machine - then, you better rent.
When is the wedding again? I can possibly call and check for you, if you'd like.