There wasn't any foam included when I got the bike with the skid plate on it. I should order some new foam from Works Connection, though, because that area definitely gets filled with mud.
I got the chromoly plate and tubing from Aircraft Spruce in Corona, CA. I used 1-inch, .120-wall tubing which overlays perfectly on the 3/4-inch stub tubes on the frame. Plate was .080-inch thick.
You can probably find round chromoly tubing (or DOM, which is high-grade mild steel and does not have a raised seam on the inside) locally to you, but chromoly plate is harder to find.
Aircraft Spruce is great at shipping things and fortunately you wouldn't need that much tubing or plate to duplicate what I did.
Other relevant details: I did all the plate cutting, drilling, and forming with basic tools. I used a band saw and drill-mounted hole saws of different sizes. I did the sanding/grinding with a stand-up belt grinder (similar to a Burr-King) but the same results could be achieved with a hand-held die grinder or an air-powered grinder. The main point is that no plasma cutter was involved.