That's a really good looking piece Lons.
Though I don't do much of it I like working with copper (sheet). As a matter of interest, all the stuff on rooves here that would be lead flashing in the old days in UK is sheet copper over here (as are many rainwater gutters and downpipes). In fact I think the only bit of plastic guttering and downpipe in our road is on the 2M square garden tools storage shed I put up a few years ago!
I therefore keep and eye open and have managed to piece up a nice couple of bits of "scrap" sheet copper whenever I see work going on -there's another refurbish going on in our village right now and I guess it's very near to tiles and flashing time.
Anyway, I do have some "scrap" copper sheet offcuts stashed away. Keep the size reasonable (for postage) and I'll happily cut off a couple of bits and post them to you.
Re copper rivets, unfortunately I couldn't open the link in the post above, sdo am not sure exactly what was being referred to, but from what little I know, copper rivets are available in all sorts of lengths and diameters. Try a couple of the Model Engineering suppliers shown in the sticky list at the top of the General Metalworking section.