I had the same problem with pizza stones so I went to the local metal fabricator store and bought a new piece of 1/4 inch steel.
I had them cut it 14x16 and then cut about one inch from each corner to kinda round it a little. When I got it home I took my hand grinder to the edges to round them over a bit, and then then took a brillo pad, soap and water and scrubbed it to remove the oily film.
I then seasoned it on my Genisis like a cast iron skillet. With that dimension, I can put a fire brick on edge under each end to raise it from the coals and the lid will fit over it but is has to be centered. It works great. Just don't drop it on your toe. Those dimensions are what I came up with but you could go a little smaller and it might even work better. I can't remember the cost, but it wasn't bad.
Also since this is flat, a peel works well. I wasn't sure how a cast iron pizza pan would work with the peel because of the raised edge.