They are $2 a set at http://www.biketoolsetc.com.
My local bike shops had most sizes in stock. You will want to get the right size.

Did a set recently following the advice given by Sheldon Brown on his site (Support the crank with a pipe before beating on the pins, etc.). Re-used my old ones. Just loosened the nut a bit before banging on them, so the ends did not get flattened too much.