try napa? they have alot of oddball parts, maybe an electrical supply store? a real one not menards or lamp depo or something i mean an industrial place like fastenal, or grainger.
sometimes old old hardware stores still have a variety of bulbs around.
i know you said physical store but amazon has a 10 pack for $8...
http://www.amazon.com/10-PACK-Eiko-M.../dp/B003JW0F2E
macs for buck a piece
http://www.macsautoparts.com/ford_tr...t-bulb-51.html