Or grind up a few ol pennies
As long as you use pre-1982 pennies.
I once had a hollow pill that was a PERFECT fit for press fitting Pennies (as scaru mentioned, pre 1982)
BTW, there is a direct relationship amongst metals, between its electrical conductivity and its’ thermal conductivity. In other words, metals that a good electrical conductors are also good thermal conductors. it is called the “Wiedemann-Franz Law”
“the correlation between the heat conductivity and electrical conductivity of metals.
In 1853, G. Wiedemann and R. Franz (1827-1902) established on the basis of experimental data that for all metals the ratio of heat conductivity K to electrical conductivity σ at a constant temperature is the same:”
(from the from The Great Soviet Encyclopedia (1979).)
I learned this in school, but always thought it applied to all materials.
I recently learned on this forum (BLF) that this law ONLY applies to metals!
Diamond can be 5 TIMES better than pure copper for thermal conductivity!
Diamond and Silver torches, now your talking guys! Bling it on! But my bank balance will hate this. 
On another note, vampyre hunting lights anyone? 
I have never melted copper but aluminum is pretty easy to do with a propane torch and a crucible made from a large brake piston. I have a ton (well, a quarter of a ton) of zinc and zinc is even easier to cast but has a poor thermal conductivity.
I’ll toss this out as another alternative. Check w/ local metal roofing shops. They use copper sheeting for flashing, it comes in various thicknesses. I got a big 2’ x 2’ bit for $10. Its dead soft so you can use a punch or shears to cut to shape.
How thick is your piece?
2’ by 2’ is really big for only $10.
At Home Depot, they now chain the rolls of copper flashing to the shelves. (signs of the times)
Our house has copper gutters and down spouts, It cost me $500 for parts to do a small I repair that I did myself!
I had to do it myself, because I couldn’t find a pro to do the job.
On another topic here on BLF, Chicago-X showed off a 20lb hunk of copper. Now how much did THAT cost?
I know that I am just curious how thick it is, which you have not said as of yet.
Around the same as a new Fenix TK41, after BLF discount. 