Hi Smoke 73,
You could try an electronics supply shop. They may have 4% Silver solder.
I can buy that here from Dick Smiths and they also have 99% Tin, lead free solder, in small flux cored rolls for the home electronics builders.

Try the welding outlets as well. Commweld here, has 200g rolls of 6% Silver 94% Tin un-fluxed and I use that for soldering island sight bases on. The 4% is strong enough for the banded type.