A hard solder commonly used on copper is Silphos. It is mostly copper,
but with a little silver and phosphorus. Plain propane is hot enough,
but with the size of your part you will either have to figure out a way
to keep the heat from escaping or use multiple torches ( or both ).
If I were doing it, I would use some insulating firebrick to surround
the part and a couple of propane torches. I prefer the rods with 15%
silver over the ones with 5% silver. The Silphos should be available
at any welding outlet and probably at a plumbing supply house.

Get some and try it out on some scraps of copper.

As for where to get copper...........in Seattle try Alaskan Copper and
Brass.


Dan