David, I made "diamond plate" for my K-27 by making a sandwich of three pieces of styrene cut to a shape that fits what I wanted in the cab to tender area. The center section of the styrene sandwich is shorter by 1/4" on the cab side so it will slip over the existant small cab plate. These styrene pieces are thin so the three piece laminate is not to thick. Then I cut some screen wire to over lay the three piece laminate laid on a diagonal. I used acc glue to fix it to the styrene and filled in the screen pattern with additional acc glue. The acc glue laid down really well and filled in nicely so as not to leave too big a diamond plate appearence. Then paint black, looks like it was made for it.
Additionally I drilled a small hole in the this extension piece and glued a small brad nail up through the floor so I could place a figure standing on the plate with a shovel as though he were up and at it. Just drilled a small hole up the leg of the figure. He can be left to swivel on the brad nail to change position of shoveling.
Dave, I obtained etched brass sheet for a deck plate from: E.M.A. Model Supplies Ltd in England. If I remember correctly, their website is: ema-models.uk. The sheet is only about 0.008" thick, so it must be laminated to something for strength. They have a selection of patterns; the "diamond" pattern is actually squares on a 45 degree diagonal, each square looks to be 1mm.
Using Google, I could not find a domestic supplier; if anyone knows of another source of stuff like this, I'm interested.
I have been hoarding and stockpiling scale diamond plate for a while now. I think diamond plate is cool stuff to have on hand so when I find it I get it. I have some nice stuff that I bought probably 10 years ago at a hobby store in Minnesota. It was sold as 1:24 scale diamond plate to put on model fire engines, truck running boards, etc. I used it here as brake pedals on my 1:20.3 scale donkey engine.
Unfortunately I have no Idea who manufactured this stuff or if it is still available. A search online for model truck/fire engine accessories may yield some results. As you can see though, this stuff reflects more modern diamond plate. The other stuff that is a bit more easy to find is made by K&S's special shapes division. I used some of it as a tender footplate on my Regner Konrad bash:
This stuff is available in various sizes of diamond tread. I find the largest stuff to be best for 1:20.3 scale. As you can see this stuff has the diamonds all oriented the same direction which is more indicative of earlier vintage treadplate.
If you can't find what you are looking for you can always pick up the metal etch kit from Micro Mark and have a crack at making your own.
Back when I worked at Niagara Hobby in the Buffalo NY area they carreid not only plastic car model accesories but military model accesories too. Don't bother calling Niagara i was there this weekend looking for stuff and they no longer carry those accesories. (sigh) They actually no longer carry a LOT of things, another story. But if your searching, do not rule out the military model accesories.