Thats a very good question because there does not seem to be any agents for Commercial unit renting. Probably because its difficult to see how you could make a profitable business.
I think you will have to drive around the areas that interest you and call the numbers on the Se Alquila?s
Good luck
PS I strongly suggest you use a good solicitor before signing any rental agreements - a client of ours nearly signed up on a unit until we discovered that it only had internal access and it was only for a residents community!