I bought a Pro-q stacker off of eBay that fits well on my old Jumbo Joe, not sure if it fits on the new ones. It has to be inverted to fit but it works. Sorry, no link but you can just search on eBay.
Co-head cook of Smokin' Timbers BBQ
22.5 Weber Kettle Grey, 22.5 Weber Kettle Green, 22.5 WSM, Two 18.5 WSMs, Mini WSM, Weber Genesis Silver, 18.5 Smokey Joe Platinum with Pro Q Stacker, WeberImperial Sequoia, Charbroil Silver Smoker, Rib-o-lator, Green Thermapen, Stoker with wifi