If you take your VIN to a Jayco dealer, they should be able to look up the tank for you. It will take time to get (3-6 weeks) but it will be an exact fit.
Aftermarket tanks are out there, but you need all the measurements (L/W/H side drain or end drain, with or without sensors.. etc)
22 Year Air Force Civil Engineer, Retired.. Generator Tech at Grand Forks AFB, Part time RV Tech and Parts Manager at a Jayco Exclusive RV Dealership