it is good to be on a forum with expertsWe go over this every few months.
In the US you can use FindChips.com Search to search for parts.
First level suppliers are DigiKey.com, Mouser.com, Newark.com, and Allied.com.
Surplus places include Allelectronics.com, AllTronics.com, Electronic Goldmine Jameco, JDR, and MPJA.
The are several places that buy and resell parts. Arrow and area51 come to mind. Expect to see a $50 min order from these places. Can be a last resort for obsolete parts.
Futurlec is sort of in a class by itself (so far as I know), cheap and slow.
For Microchip parts you are order fromWelcome to microchipDIRECT. I so nor know if Atmel has a similar site.