From the top of my head. Get scrapebox, add relevant keywords, scrape it all, then use PA/DA checker plugin into scrapebox, let it check DA. Then if you want, run the domains you like via some free majestic tool that will also tell you their majestic topic, because there will be some non relevant results.
Or search for them manually.
Ahrefs or other paid options would be fairly effective, but unless you have either paid Majestic or Ahrefs, then using Scrapebox (which is paid, sure, but it's a swiss army knife of SEO) is the best option.