Robert,
Try here:
http://www.metalsupermarkets.com
They have an outlet in Burnaby. We buy pre-polished sheet all the time and I think that's where my guys order it from. Otherwise, look for any commercial metal distributor. It comes in 4x8 sheets (usually) but only a few thicknesses, and at Metal Supermarkets, they will sell/cut as required.
Good luck!
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