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.