If it is a silver soldering problem you could try Castle Steam, they advertise as model boiler makers but I know they silver soldered some very complex assemblies for a friend of mines company on a repeat basis, he spoke very highly of them. I believe they started out making laboratory equipment or similar and then got into boilers as a result of their SS experience.
Alternatively if you need SS advice CUP alloys are very helpful with advice on all SS matters.
Dave