Hi Jon,
This post baffles me!
Why would you want to make joints at 1000°C , probably using a fine hot flame (oxy acetylene?) when you can be using simpler equipment and making your joints at a considerably lower temperature.
You would also be able to use more readily available filler metal with an intrinsic value of approximately 50% of fine silver. What's not to like?
Are you simply looking for a cheaper method of making your joints?
Can you get fine silver fuse wire from say your local DIY shed? Don't try to explain what you are trying to do 😀
Find a supplier to the amateur silversmith for the rods and wire. However they tend to restrict themselves to standard or sterling silver and not fine silver. Don't expect their overheads relating to distribution to be any different!
Then follow Dave's advice.
Regards
Keith