I bought Weber hinged grates for my Jumbo Joe at Target at the end of the season on clearance. I'm 99% sure the grate is 18.5" and can be bought anywhere: https://www.google.com/search?q=hinged+weber+grate+18.5
If you have a Home Depot, Ace or Lowe's close by, bring your Jumbo Joe to be 100%...