FWIW, on an 18 WSM, a standard size grate will kind of fit on the bottom, but will rest on the bolts slightly above where it is supposed to be. If memory serves, you have to tilt it somewhat to clear another set of bolts a bit higher up on the strips bolted to the body that hold the water pan & grates. I don't know if the same is true for the 22, but you might try it out with the grates you have on hand if you otherwise cannot get one that is quite the right size.