If you are not lucky enough to live near a Fry's Electronics you will most likely need to order your electronics online.
FindChips.com is a great online tool for finding a vendor if you know the part number, if you don't you can try from the list of vendors below.
Digi-Key is the first choice for electronic components.
Electronics Goldmine sells random electronics, often refurbished or pulled from discontinued products. The website is a great place to visit for ideas.
Jameco is usually the cheapest, if they have it. That old adage about price may apply.
Mouser Electronics, Inc
If Digi-Key does not have it Mouser might.
If you still can not find the part try Newark, the shipping and handling is usually more expensive.
They sell cheap electronics kits and a great source of motor controllers. Their website has a ton of information about basic stamp microcontrollers.
Sparkfun is a great small business that specializes in hobby electronics and kits. They have tons of sensors and tutorials.