You can get one on the Tiffin store web page, but hold on to your socks. The cap is very expensive, the Tiffin sticker for the center is also way too costly, and the shipping will water your eyes. If you can do without the center sticker and live with a polished stainless "Baby Moon" you can get one for less than $10.00 at a truck chrome shop or a NAPA or similar. Mine was $8.95 at a local truck parts place. And you can't tell you're missing the sticker as you can't see both wheels together to compare.
2013 Tiffin Allegro Bus 43QGP
2011 Chevy Silverado 1500 Toad