I live in Toronto Canada, and I have ordered from Sculpture Supply Canada and they are great, highly recommended. I purchased my Epoxy Sculpt from them. Try to get the colour that matches your sheeting and cubes, I got black.
You will probably want a razor saw and mitre box, check your local hobby stores for these, there is a combo pack that contains both. Wet sandpaper in several grits leading up to as high as possible to get a very smooth finish and try a final polish with regular bond paper. Any sort of super glue should work for affixing your sheeting.
You will want styrene or ABS sheeting 1-1.5mm thick, you can easily order at several places online, including amazon, check local model and hobby stores that might sell packages of 3 or 4 sheets, which is not too costly. Or you could check out local plastics manufacturers or distributors.
You may have to purchase a larger amount, but its cheaper in the long run. I got mine from here: http://www.lairdplastics.ca/locations-list
You might also want to pick up some vinyl in different colours, try your local art store, usually around 5-7 dollars/yard. If you don;t want to trim your own vinyl, you can purchase stickers at a place like cubesmith.com.
Google and a telephone are your best friends.