While this has been addressed several other times on other postings, here goes.
Options:
1. contact an official chip reseller and browse their site for just the pin header and purchase directly from a reseller.
2. go to your neighborhood electronics part store and/or hobby shop and pickup a 16 pin (or larger) pin header.
With option 2 you will need to remove the unused pins. Note, the pinheader should not have a shroud around the pins, if it does then you must get a 16 pin header. Also if the header has more than 16 pins, then you will also need to break off the extra pins & the plastic portion attached to the additional pins.
The pins to remove for a 1.6 or 1.6b board are 1, 11, & 13, while for those boards <= 1.5 should only remove pins 1 & 13 from the 16 pin header. Make sure that the header you select is designed for soldering and not wire-wrapping.
Pin layout:
(16)(15)
(14)(13)
(12)(11)
(10)(09)
(08)(07)
(06)(05)
(04)(03)
(02)(01)