1996 LX Addon Slider Windows

I was looking to buy an '01 Ford Escape because of 4 windows and doors. But after finding that I owe more than my '96 Windstar is worth I want to add slider window on driver side for my 7'L 36"h wolf dog who likes/needs to "breath" the air. I looked on internet using many keywords and don't see any add-on slider windows for the Windstar. Can you help? Thanks.