I know many people have asked where to get metal foil on this forum including myself. No one makes lead foil anymore except for the medical and nuclear industries. Why?...because well...it's lead! Anyway, I found this online retailer: http://www.whimsie.com/index.html
that sells copper, brass and aluminum foil/sheets in 4-5 different gauges(thickness) starting at 36 gauge (.005") to 18 gauge(1mm). You can also buy 3"x3" samples for $3 or a 5 gauge samples set for $16 (these prices include USPS Priority Mail). They also sell copper wire in every gauge possible. It's probably better than cutting up a tube of Thome's natural toothpaste.