Hi,
I would suggest that you take a tape measure to a bbq shop and begin looking for a grill with a 22" diagonal measurement. When you find a grill that will fit, you can then call the manufacturer and purchase a replacement grill.
Some years ago I purchased a CharBroil replacement cast iron grill that fit perfectly in my Weber kettle. I think it was 17" X 14" in size. Over a period of time, it began to flake heavily leaving cast iron residue on my steaks.
Three years ago I purchased a very heavy stainless rod replacement grill that also fit my Weber kettle. This is far superior to the cast iron grill. In this case, I had to round the corners with a bench grinder to achieve a good fit.
Tim