Glenwood, I ended up ordering a piece of 24"x 24", 20 gauge sheet metal on line. Hopefully it will be here in a 3 or 4 days.
Threewood, at least there is someone local you can deal with. I am a pipe fitter and you would think, our sheet metal department would have some 18 gauge laying around...but, they didn't.
Wmlantis, keep you fingers crossed and say your "prayers". I am pulling for you buddy. The area looks pretty good. Hopefully, that is all the holes that will need to be dealt with. Usually, after removing the rust, either with a wire cup brush on a side grinder or sand blasting. It usually ends up looking like "Swiss cheese". If it ends up looking like Swiss cheese, learn laugh to keep from crying. I have done the "laughing part" a lot on this restoration. Another option for rust removal, that is less destructive, is naval jelly, steel wool and a lot of elbow grease. This process will save as much metal a possible. Good luck and keep us posted.