Realtors get about a month rent from the owner for finding a place, that is very little money, so they may ask for a fee to find it for you. When you know where you want to live, drive around and check for a rental sign (Se Alquilla), or check the clasificados.
Realtors do not do that much with rentals, and are not going to drive you around the island hunting for one. It is a quick operation mostly, show you what they have and you go see it and if you like it, come back to sign the paper. If you instead deal with the owner you can negotiate and maybe lower the price or get some used furniture out of the deal.
Condo rental they are likely to have handy, houses some. People put up a sign, they tend not to use a realtor.