I am running a Marathon motor on mine, perfect fit and smooth operation. Item # 4782 from www.marathon-motors.com
Here is the EFM dealer locator. http://efmheating.com/dealer-locator
The grates usually aren't a sudden failure item...the ones I have seen get fatigue cracks before they totally come apart. You can get a full set if you want, but a couple used ones might serve the same purpose. 1/4" gasket rope is used around the top ring and between the plates and the ring. You can use 1/4" on the bottom lip of the plates, but I prefer 3/8".