At your welding supply chances are they likely will not have a clue about what you want or are trying to do. If they have silver at all it is probaly going to be Harris 56% because that is what the HVAC and food service maintance guys like to use. Brazing rods are likely going to be bare brass or blue fluxed nickel bronze because many of the tool makers use that.

Best thing to do is stop in at the welding supplier and have a look around to find out what the brands they carry and then google for the manufacturer's website, all of them will have data on and descriptions of their products. Just be aware that many suppliers sell rods in 5lb packages and if they special order for you it may be a 20 lb minimum, Silver is usually a mininum of 3oz troy. Some of the bicycle tubing suppliers may have brazing supplies in smaller quanities. Try googling: "Josh Putnam" he is another amatuer builder and has(or had) a list of suppliers on his website under his framebuilding subtitle.

This is the stuff that works well for me; your experince may be different.
I use Harris Safetysilv56 with Harris white flux for most lugged joints. on bottom bracket and fork crowns I use the higher temp black flux since it takes longer to get these thicker componets hot enough to fill.
For looser joints like dropouts and lugs with more clearance I have good luck with Harris Safetysilv 45.
For fillet brazing I use Gasflux brand rod #C-04 with Allstate 11 flux or Harris Black . The C-04 rod is apparently a popular rod for fillet brazing.
The nickle bronze I like is Harris #40 FC it is precoated with flux and is great for quick and dirty work like punk and junk bikes. I repair most everything ferrous with this rod. if you scrape off 2/3rds of the flux it will make neat strong fillets also but not the big fat ones like the C-04.

Some additional reading about brazing and amateur frame building is found on Mark Stonich's excellent website . http://mnhpva.org/tech/gear_head.html


Some final word of advice to anyone building for the first time: IMO stay away from the thin exotic steel tubsets till you get some skills. All of the failures I have seen by home builders have been with the lighter gauge heat treated tube sets. Overheating weakens heat treated tubing and the thinner the tubing is the easier it is to overheat. IMO heavier gauge non-heat treated Cro'mo Tube sets like 525,RC2, Deddi Zero Uno etc are more forgiving to overheating and mishandling and is a sensible choice for beginners.

have fun!