The best source, if you can't gather the MLS in CSV or XLSX format is to go to the county appraisal district and get the list for free. It might take sometime to filters it or you might get lucky if it's the way you need it. But you can get everything you could possibly need at the county if you do it right. Depending on your county it could be a little difficult to parse the many different formats they have. But if you get it right you can have everyone in the entire county (buyers and sellers) up-to-date. Some counties won't have their numbers and if they do they aren't always correct. I have been able to have a significant amount of records across 4 different states.
Listsource is a great option if you would rather just pay now and not have to worry about it. I don't know about Datatree. You would have to use a different service to get numbers. But beware of some companies marketing to your list after you paid for the numbers. Just look around and see what companies would best suit your situation. They can give you 3 to 10 numbers. Some service gives you 3 and others give you up to 10. Hope this helps! Let me know if you have any questions.