Editors generate those lists primarily from their own market knowledge and that of the editors and the marketing and sales staff that surround them. To check if they’ve missed anything, they turn to a source available to you, too: Amazon.com. Go there, type in any similar titles you can think of or just type the topic and genre into the Book search field (i.e., “tanks memoir” or “vampire young adult”). See what appears. Click promising titles and consult their “Customers Who Bought This Also Bought” sections. Now click on the reviews for relevant Also Bought books to see if the reviewers mention other books. Follow those leads. Also, ask your writer’s group if they know of similar books, and ask the staff of the independent bookstore near you, too. If it’s a children’s book, ask your children’s book librarian.
This targeted search is no substitute for developing your knowledge of the marketplace long term. That’s how editors spot a fresh idea when they see one. At a minimum, you should be getting the free Publishers Lunch enewsletter every day. Bump that up to a Publishers Lunch Deluxe subscription to learn which editors are buying which projects from which agents and for (generally) how much—that way, you’ll know your competition before it even hits the market.