Waterblocks?

O.K. I am feeling brave and would like to bmake my own waterblocks I have been looking hi and low for someplace that I can buy a good sized hunk of copper , master-carr has some but at there price/sizes ,it makes me look a little harder for a better price (that is the Idea of building it myself).I have made one out of alum. last night at work while it was slow,but I would like to use copper . Oh yes the point where can I find a piece of copper @ 3/4thk X 3" X 4" or longer so I can make a norhtbridge cooler and a vidio card cooler also ok done? P.S thank you in advance for any help.