I am guessing that there is little to no chance of finding one.
It just wouldn't be practical, the way the maids shlop water on the floor when mopping it. The futon would be rotting and smelling in no time at all. which is probaly why carpeting is not very popular either.
I bought one at La Sirena in Santiago not too long ago, as I recall I paid about US$125 for the base and $100 for the matress. (peso equivelant) I won't say these are top-of-the-line (closer to the bottom) but they work, and are not uncomfortable to sleep on.