You can buy NiCopp by American Grease Stick (AGS) online here:
Advance Auto Parts This is the best price I've found and I believe this is made in USA.
I've used a couple of rolls of 1/4" on my '54 2-ton project and have more ready to use on a '56 GMC 1-ton.
It's easy to flare and easier to bend and install than steel.