Should be able to get 30x40" mount board from jessops or any art shop.
Usually in packs that are white one side and black the other. The black side can be useful to add shape with the lighting or use for the background with lighter colors.
One thing i did make once which might be good for you Jon is -
1. get a Large cardboard box, like from a tele
2. line three of the interior sides with tin foil (spray mount works awesome for this!)
3. use some black or white felt to line the bottom side.
4. light through one opening using either a sheet of opal perspex (like i did) or anything white and translucent.
5. can also add light from the top if you want
Gives you a nice strong overall lighting, colors are bold, and should bring out the sparkle in metallics/metal flakes.
Yo can create all sorts of great lighting with things around the house.
Check
http://www.strobist.blogspot.com/ for handy DIY tips!