"The Marketer’s Guide To ACR" has a rundown: https://www.adexchanger.com/ad-exchange-news/the-marketers-g... . Of those who sell the raw data, Inscape (Vizio) and Gracenote (Nielsen) are the largest: https://www.inscape.tv/, https://www.gracenote.com/video/media-recognition/

inscape.tv (every vizio tv, that's why they're so cheap), nielsen (gracenote), ispot.tv, samba.tv, alphonso.tv, 605.tv, placed.com, truoptik, and others

Many double as ad/analytics platforms but they'll gladly sell viewership data.