Staybrite can be made into thin ribbon with a hammer. Welding
stores do sell small quantities of it in blister packs that include
a little bottle of flux.

Staybrite is available in several different sizes diameters from very
thin to fat and in several package sizes as well. I found it on
their web site and then ordered it via a local welding supply company
via the phone.

PM research will sell you 1 oz and a bottle of flux for 8 bucks.
One oz is considered enough to solder one of their boilers!

chuck