Define "larger quantity". Your supplier can order you larger packages from the wholesaler, like one pound bags. Brewing salts are used in such small quantities for a batch and are not all that expensive to begin with, so how much money are you expecting to save here?
well i'm just tired of buying mini bags of powder....rather have like a pound or so of that stuff and be done with it for a while. Nevermind...found my answer online
Have you tried asking your homebrew store for a larger quantity? I know my shop sells the stuff by weight, so I don't think they'd mind selling in larger quantities. That may save you on shipping. The stuff is pretty cheap, I would think any savings would be minimal.