I ordered a Lexan version for our last 5er from here: EZ Tops World Wide manufacture acrylic and Lexan skylights and domes.
. Great size choices, several colors, clear, smoke bronze, decent price and shipping costs. They will take at least 3 weeks to get it to you. Oh, and our new 5er needs one too (crappy installation by the factory - stress cracked across a corner) and it will also be ordered from here as well as the Keystone replacement part would be the same easily broken acrylic.
Dave W along with my DW, Susan and our poodlepups, Callie & Molly,2011 Ford F250 6.7 CCLB, 5er Hitch Option w/B&W Hitch,,Ride Rite air bags, 2014 Montana High Country 343RL (38')