Looks good - thank you. I see from their website that they have Sil-Fos" solder which lead me to that manufacturers site "http://www.silfos.com/index.html" where I found "Silvabrite" (Clean & Brite) solder which appears equivalent to Hi-Force 44 - 4% Silver, 96% Tin, flows at 430F. From the technical document, note the different fluxes recommended for different base materials: "Silvabrite alloys provide satisfactory color match for stainless steel assemblies. When used with TEC flux or Liquid Solder Flux, Silvabrite alloys will readily wet stainless steel base metals. Silvabrite can also be used for copper, brass or steel base materials when paired with Silvabrite Paste Soldering Flux/Clean ‘n Brite Flux."
If you go to the "resellers" tab, they appear to have numerous vendors in most Canadian provinces, as well as an office in Ontario.
I would be hesitant to use "silver solder", Hi-Temp, Silver braze on gun barrels - I note their melting temps are 1,100F and more. Would require heat sink? Packing bore to prevent scale? Re-tempering/heat treating?
Regarding borax - I just looked at my box of Arm and Hammer washing soda - it is Sodium Carbonate, Na2CO3, not borax (Sodium Borate Na2B4O7·10H2O), so maybe there are various products referred to as "washing soda"?