In October of 2010 we gave a donation to the Down Syndrome Buddy Walk, where do I get a letter of confimation for tax purposes, thank you

Without knowing where you are this is impossible to answer. There is no central office that keeps track of contributions across the Country.

Call the organization or organizers in your area.

You don't need to submit one if it was under $250.
Just keep canceled checks, receipts, etc in your files.