I make my own solders. It’s just like alloying any metal.
Just be causious that the really low melting alloys should be added last as you do not want them to burn off. Melt for eg. the silver and copper, move the flame, wait a little bit then add the zinc, then slowly heat it all again with slightly less heat. You’ll notice when it’s too hot for them as they will start smoking. Pour it into an ingot, then roll it into sheet or wire. Easy peasy.
The main thing is not to be scared about messing anything up. Try and try again. You’ll be happy that you won’t have to rely on purchasing solder. You can even come up with your own formulas.
Here is what I use:
75% FINE SILVER, 22% PURE COPPER, 3% ZINC
70% FINE SILVER, 20% PURE COPPER, 10% ZINC
65% FINE SILVER, 20% COPPER, 15% ZINC
EXTRA EASY 630-660C
FINE SILVER 55%, 22% ZINC, 21% PURE COPPER, 2% TIN