Get someone to use a micrometer for you to measure your existing material if you don't have one. You can then find some aluminum or plastic to use. If you get what you need, aluminum can be anodized to a nice black black once the cutting and edges are filed and smooth and the windows are milled out. Make sure all edges are sanded well with a file and then some very fine wet or dry paper will do the trick (3M makes black automotive stuff for fuinishing paints).
For sheet aluminum, use a backing board of thin plywood so you don't kink the material when cutting.You may need to use one on front and one on back (1/8" or 3mm) and some clamps to keep things flat and safe while working on it. Do your layout on the plywood and have at it. tim