Having fruitlessley searched the net, does anyone know where I could get some solid square acrylic rods. They would need to be opaque black, and have a base of 20mm x 20mm, and the company must be able to supply to the UK.
Layer 4x5mm thickness is how I would do it? Or get rod and plane to 20x20 if your confident in a jig or something
Opaque black would not exist like that. I agree with mat0tam, you will need to glue and shape your own from black sheet stock. You could get Delrin in black rods, but it won't buff out as glassy as plexiglas.