Car rental advice for Iguazu Airport this august

I am having two issues in my efforts to rent a car in Iguazu Airport: there seem to be very few vehicles (both Avis and Hertz have none) and the rental offices close at 15:00, while my flight arrives around 18:00. Is there a smarter way to rent a care there?

We want to pick up the car at Iguazu airport on August 6, and want to drop it off at Posadas airport on august 11, 17:00.

Thanks in advance for any guidance!