Q:

Set location for liberation missions? 

I have been wandering for a while around the map trying to find liberation missions to get more assassins. 
Is there a set location for the missions?  If so, is there a map I can get for the places of the missions? 

A:

They are only in Boston and New York
There are 3 Missions in each district
You can find more detail on each one here:
http://www.ign.com/wikis/assassins-creed-3/Liberation_Missions
There are maps included in the link.