DigiKey Corp. 1-800-DIGIKEY, part number CP 2090 ND $1.65
The only problem is that they have a minimum order and shipping charge. The
good news is that they have a "sample department" and if you sound official
enough and business-like you may be able to get one for free. Be prepared to
receive their large component catalogue for a few months, though.
Also I have been reading about some difficulties some folks have been
experiencing with the battery recall and would be interested in hearing
from you if you have been having problems.
Michael Crestohl
mc@northshore.ecosoft.com