The resort boutiques/sundries shops will have them as will some of the small shops downtown at the Renaissance Mall as well as new malls on Palm Beach. I am guessing the size selection will be limited and the price will be expensive.
Royal Plaza Mall downtown, the street behind Royal Plaza and on Caya Betico Croes (mainstreet). I would suggest taking the time to purchase a suit at home as there is not a big selection, sizes and in resort shops the prices are high. The reason for a bathing suit is to wear it on the beach. You don't want to spend valuable beach time running around looking for a suit.
Baby Beach -just to be lazy and float on my raft and snorkle too
Jc Penney at our mall had swimsuits for $1.97 that were over $30 this summer. Check the clearance department at Jc Penny, Target, Sears, etc. You can even try on line. I find it difficult to find any swimsuits in Aruba. We tried one year for an extra when my top buckle broke, forget that.
In the hi-rise section the stores are expensive, but by the downtown area there were these little shops on the right (water side coming from the high rise area) and the people will make deals and everything.
I personally went to Kohls and found a suit on the clearance rack. Lucky me.
I have two teens and we always buy nice suits on vacation -- we fly with a few. But its our tradition. And I hate having to look for suits. I couldn't believe in Jamaica and Cayman we had trouble finding shops that sold high-end suits.
Some of the best suits we've purchased are from South Beach FL--