I got mine at Home Depot. No one there knew what expanded metal was. I found it as I was walking in the cement supplies section. It is used for plasteing also. It is not as heavy duty as some of the pieces I've seen here, but $10 for a 2'x8' piece it's worth it. I can make 6 or more fire boxes out of it.
Chargriller Pro w/SFB 3 generic digital thermometers