Torrentleech will open signups usually on ebery major holiday and around black friday. Or look at r/opensignups and related pages on the web to join one which interests you. Other trackers will do usually do that on an anniversary or by invite forums on affiliated trackers. And for those forums you just need to meet the required ratio/upload and account age. But those “high value” trackers are rarely worth it as most content will trickle down to the lower tiers with lower requirements. Specialty trackers are hard and rarely worth it as well (except if only they can get what you need).