Small screws can be expensive when purchaced at hobby shops. Six screws can cost $5 or so. I get my screws from Fastenal. I have to order the screws but have them in a week or less. It's about $3 for a hundfred screws of 2-56X1/4". There may be other suppliers so if you know of a source let us know.
We don't have that brand name, but there is another here in my town. I have found some nut and bolt supplies there for my modular needs. Much cheaper than any other area source.
I've discovered the same thing and purchase #2 through #10 size screws in several lengths for much less money than buying them 4 at a time from the hobby store. We have a Fastenal store and two other places that sell things like screws in any size and head style you can think of as well as things like drill bits and other good quality small bits of hardware. they stay busy and I'm glad there is such demand for them. It's one place I can save money on something I use a lot of. Rick H.
Try McMaster-Carr - they have about ever imaginable screw/type/material you could ever want. http://www.mcmaster.com/#machine-screws/=yr88ap
How about the local Grainer store? Have one in town, just not sure what they carry. Could use a source, for the screws used by USA and Aristo Craft, for joining their G Scale tracks together! Or for the Split Jaw clamps I also use, to hold my track together. Be nice to have back ups and replacements as needed.