What you are looking for is called Texalium (brand name Hexcel Texalium) and is commonly sold as "silver carbon fiber", but there is nothing carbon about it. It is aluminized e-glass.
This is the cheapest (and thickest) I have found - http://www.robotmarketplace.com/products/carbon_fiber_silver_hex_sheets.html
Be warned though - it is usually double faced with a carbon core. I have seen kit scales of it on Knifekits.com, but they don't seem to have it in sheets. Their scales were texalium all the way through though.