My experience as a RV part dept guy showed me that most RV tail lights were RV brand non-specific. That is, usually you could find the tail lights from most any brand camper in the parts catalogs. Even though the dealer I worked for was not a Jayco dealer, I could get about every style of tail light found on Jaycos. That is if I didn't haven't on the shelf already.
So I would try the most convenient dealer to you, and see if they can match the lens you need.
FAA A&P mechanic, ex-RV dealer parts dept
Retired B-52 Gunner/Flight Examiner, B-52 Crew Chief
2016 Jayco Eagle HT 29.5 FBDS w/ 15,000 BTU AC, 50 amp service, upgraded counter top, thermal pane windows, elec. stab jacks, outside grill, backup camera and MORryde pin box.
2011 GMC 2500HD DURAMAX/ ALLISON