I have one of Kyle's cab tops, and it's held up pretty well over 7 years. I'm not sure if he's still in the business, however. When I got mine, he was working just down the street from Dennis Williams' shop. If you have trouble finding him, you might check with Dennis (Linden Eng.)
If Kyle is a dead end, I know that Bob Rainek bought several of those tops. Perhaps he's still got some around. Here's his website, but I can't even speak for whether he's still in business or not: http://www.buypinzgauer.com/
I've only seen three or four Pinzgauers with the plastic side panels. Every one of them had cracks in the plastic some were. If you end up with one I'd spray some sort of stiffening foam on the back side.