I think any large user does go direct, and a lot of builders go direct. But that's not going to work in small quantity. The customers at the LWS either use silver (Heating contractors, I think) or they use MIG/TIG. I don't know that there really ever was a widespread application of bronze that would lead the LWS to carry a decent supply of high quality stuff. At one time, there was better choice of silver, I think that has gone away too now because of TIG.

the good news is that flux and filler last a good long time, although on bronze you should remove the oxides with a scratchy pad. You might have to add water to flux if it has been sitting around for a while. The thing you have to ask yourself is what is the price of frustration?