This is a great question! Voting records from the first Congress (1789) to the present are voluminous and tracking every vote will be a large undertaking. We can't provide a comprehensive list of every unanimous vote; however, GovTrack is a great resource to find the information you're looking for. Using GovTrack, you can filter votes to a specific Congress and sort the votes by "Most Supported."
You can also search the Congressional Record, the official proceedings on the floor of the House and Senate, for legislation passed unanimously.
I hope this is helpful!