In the last couple of weeks I have literally shared this on about 10 posts so thought I would just share it with everyone as it doesn't seem to be common knowledge on the forum.
This is not an affiliate link, it's not that kind of site.
This site has list brokers for every niche you could possibly think of. As most solo ads are IM based it is a great option to test your non-IM product on.
Mailing List Finder -- Search & Compare Mailing Lists
All the best,