Trivially: http://nationbuilder.com/voterfile
etc
As for "For free", states are generally required by law to give it to you if you ask. Some charge fees. Only two have crazy fees (5k and 30k) has a crazy fee (though if you challenge them, ...etc)
https://trello.com/b/IlZkwYc0/national-voter-file-states-pip...
There is a github project i'm aware of to put together all of the data: https://github.com/national-voter-file/national-voter-file