I started a thread on this about 5 years ago, still nowhere to the best of my knowedge, bear in mind the heat perspex creates, ventalation as well. You may be better off with mosquitto screen in a wooden frame. Sorry if I've misunderstood your use for the perspex.
Nothing on the North Coast, I just went through all of this and Santiago is your closest choice.
I purchased Plexiglass at Ochoa, in Santiago. The store is across the street from the main/original (?) store.
They had many thicknesses and cut to size.