Joel, I've looked for fabrics like this at Joann's and on the Joann's website. In the utility fabrics section, they have a nonwoven fabric that is heavier than Propore but looks and feels similar. It comes, as you say, in many colors. It is for diapers and mattress covers. Their website explains that it is polyester with a polyurethane membrane. I have never seen a Propore-like polypropylene/polypropylene laminate there.
You seem pretty certain that the stuff you saw is the same as Propore, but I'm a bit skeptical. Maybe it's different than what I saw.