I don’t know but the two political parties obtain them because I’ve gotten mail in various state I’ve lived in based on party affiliation.
There are a couple, three way to get a list;
You can apply to the county registrar’s office, usually a form for that purpose is available, however there is a small fee per name. But don’t be mislead. A penny a name for 100,000 names can get expensive for an individual to bear.
Which leads us to a second choice; contact a local “True the Vote” type group and see if you can get anything from them. They probably won’t share but you can accomplish the same thing as a volunteer.
Finally, the candidates all, routinely, get lists for mailing, “door knockers,” etc. Perhaps a local candidate of political party can help. You can always contact the state party committee. Again, if you want to volunteer for some on-going voter audit/review there are lots of folks looking for lots of help.