Howard,
I looked in vain for a large saucer (19"). You might find one at a specialty nursery but I had no luck at Home Depot, Lowes, etc. I found some large saucers online but they were $30! I opted for a 16" saucer from Home Depot. I had a small 8" saucer at home. I put the 8" saucer in the water pan upside down then put the 16" saucer on top of that. Foiled the large saucer and then the water pan. Works like a charm. Sits about 2" below the lip of the water pan so it catches grease/fat perfectly. Hold temps like a rock and 5 second clean up. The 16" saucer has about a 2" gap between the saucer and the water pan, but since I foil the water pan for clean up it holds in all the heat.
Think the 16" saucer cost approx $8-10.