Many people use a round grill. Many of them come with cheap grill grates and will perform better when they are used with round cast iron grill grates.
if you are a regular visitor of this website you know I love that material because of the reasons that it retains heat really well.
The second reason for me to use it as much as I can is that it is so easy to clean.
In a hurry? Find your size cast iron grill grate here!
I know that it is impossible to find every size for every brand of grill but here you can find a link to a large number of them on Amazon. I will have a look at 5 of the most sold ones for you. That might help you find the one you need.
Many of them will fit the Weber 22 inch grills I reviewed and some other ones are a perfect replacement for the Kamado type gills like big green eggs or other brands.