Check your local listings for metal manufacturers in your area. Have them laser cut a "griddle" out of HSLA plate steel. It'll be the cheapest option.

Otherwise, check out SnS, Pizza Steel, LavalLock, and Amazon has plenty of cast iron griddles too.

​

Edited to add: https://www.amazon.com/Camp-Chef-SLJ20-20-Lumberjack/dp/B000MSC6OI/ref=sr\_1\_5?crid=312N4SSV5JBLD&keywords=20%22%2Bsteel%2Bskillet&qid=1649769794&sprefix=20%2Bsteel%2Bskillet%2Caps%2C74&sr=8-5&th=1&psc=1