I'm a newbie too (2 months of "serious" torrenting) and I'd recommend that you check the open trackers section, as Katsuhiro said. Maybe you won't find what you're looking for, but there are a few good trackers that allow new subscriptions from time to time. Learn their rules, their language and build good ratios (you'll have to show proofs in the future if you want to join some communities).
If you don't want to wait for a chance to receive an invitation, the fastest option is to buy one.