A good place to find copper sheets is McMaster.com.
http://www.mcmaster.com They are a large industrial supply house.
They carry a great number of sizes and thickness, and satin or
mirror finishes. We are still looking for anyone who may have bought
Superior No.6M flux, and your reaction compared to Superior No.6.
Harold Ackeret H&N Electronics
FYI, I checked the prices on McMaster and they are a bit spendy
compared to the supplier in my local area (Alaskan Copper and Brass)
in Seattle. Alaskan sells brass sheet for about $4.25 / lb and the
prices in McMaster look something like $7. Dealing with Alaskan is a
bit quirky however.
Tom Kreyche