Another good source for this and other hobby fasters is this place:
http://www.microfasteners.com/
Ialso like
http://www.mcmaster.com
The have all sorts of useful stuff.
Every decent sized town has at least one old school hardware store with a good fastener selction too as well as stores that specialize just in fasteners. You may have to buy a dozen or so to meet their minimum purchase but at least it is available.