The NASA Near Earth Object web site (NEO) is a good source of info. Find it at: http://neo.jpl.nasa.gov/
From there one can go to the "Close Approaches" tab for additional info
including a large catalog of NEO's--both past and present.
The one closest to the time period suggested is:
Comet: 2001 WN5;
Date of Near Miss: 2028-Jun-26;
Miss Distance (Nominal and Minimum): 0.6 Lunar Distance