well, niether RooR nor Illadelph makes a double perc'd bong that you'll have much luck finding. It's also worth noting that most of your high-end companies that do percs like Toro, SG, Luke Wilson etc don't really put out many double percs, at least not stacked in a triple chamber style, it's just not really neccessary. If you're set on two percs on top of each-other though, I've seen ZOB 8 arms and Everest 8 arms in that syle, from grasscity and chicokush respectively, in the 300 ish price range. I'd look into getting a single 10 arm though, or if your price range is a bit broader, a toro 7/13 or SG inverted 4 to 8 arm.
I've heard mixed things about Zobs though, but I don't really know the details. Are they good quality?