I've bought from this company a few times - they're quick and easy.
100 Organ Brand Needles in sizes 9-20 $13 + $2 shipping:
http://cgi.ebay.com/itm/160525454265
Another one, also reliable:
http://www.ebay.com/itm/290623332675
Never used this one, but they've got fairly good feedback and they sell for about the same price in assortments:
http://www.ebay.com/itm/290420997431
These are Korean Orange brand needles, which have turned out to be indistinguishable from Schmetz or Organ brand for me over the last few months - very cheap, but apparently high quality:
http://www.ebay.com/itm/290625162732