We’ve already listed the main sources and services where you can find clean domains. You can also try our new service, Karma[.]Domains. It’s an aggregator of expired domains from various auctions and an alternative to Spamzilla. It collects domains from different auctions, calculates SEO metrics, and checks for spam in the WayBack Machine—all without a monthly subscription and with bonus credits.
Checking a domain’s history can be just as important as DA/DR metrics and others. Metrics can be artificially inflated, but the history from the WayBack Machine will show how the domain was actually used.