At the following site you can put in your zip code and find events near you. However they are ALL events, not just Kerry appearances.

http://www.johnkerry.com/events/

Also, the Ohio Kerry-Edwards campaign told me that the best way to find out is to call the Democratic Commissioner for the county, which in the case of Columbus is Franklin. The Commissioner will know the VOLUNTEER coordinators for the county Kerry-Edwards campaign, who will be up to date on the events in the county. You have to call the BOARD OF ELECTIONS for the county to get to the Democratic Comissioner.

Whew, seems like it should be easier but...