This post will show you how to sync your twitter contacts with your osx addressbook contacts.
It will add the twitter account details of the people who are already in your addressbook to those entries.
Goto System Preferences > Mail, Contacts & Calendars
add your twitter account if not already there.
once your twitter account is added, simply click on the account name in the left hand column
then click on ‘update contacts’
all of your contacts which are also on twitter will have their twitter names updated.