Derrick I got my steel plate at Speedy Metals in New Berlin, WI. It's not too far of a drive but I had my friend pick it up for me since they come down to Chicago every month. They sold a 15" x 15" x .5" for about $36.
Scott, Deb I have an old old oven with no top broiler. I've gotten around this problem by placing quarry tiles on the rack above. It makes launching pizzas interesting but it is doable. The steel plate in my set up on the second rack will hit ~580F and the bottom of the quarry tiles will hit ~550F. Depending on recipe/sauce/cheese I will occasionally have to screen the pizzas for the 30 seconds of the bake. I get about a 4 to 4:30 minute bake. I'll post some pics with my set up and some pizzas in the near future.