Here are sprockets from Small Parts, Inc. They don't have 15 tooth but do have 16 tooth which will make things go a little faster. You are looking for the #35 chain, 1/2 bore. They have the set screw and keyway.
http://www.smallparts.com/products/d...tions/rcss.cfm
At MSC on page 3720
http://www1.mscdirect.com/CGI/NNPDFF?PMPAGE=3720&PARTPG=GSDRVSM&PMT4NO=36308584& PMITEM=36684397&PMCTLG=00&PMT4TP=*LTIP
there is the 36684074 part number which has a datasheet here:
http://www1.mscdirect.com/CGI/NNSRIT?PMCTLG=00&PMAKA=36684074&partnerURL=http://catalogs.shoplocal.com/mscdirect/index.aspx%6Fpagename=shopmain%50circularid=11264% 50pagenumber=3716%50mode=
I think but am not sure the keyway is correct as is the setscrew.