Whenever I do a workshop, no matter the subject, I get writers asking about how to find an agent. There are the usual places.
Look in the books that come out each year designed to tell you about agents and editors, like Writer's Market. Keep in mind that most of these print books are pretty much out of date before they even hit the shelf. Writer's Market has within the last few years offered an online version that is a bit more up to date.
You can look in the LMP. That stands for Literary Market Place, but everyone knows it as LMP. You won't find this in your local bookstore, maybe not even in your branch library. That's because it's expensive. Check your bigger library. If there's a big writing organization in your area, they may have it. In the LMP you'll find authors and editors listed, along with contact information and what the agency represents. It's more up to date than the agent books in the bookstores because it comes out more than once a year. (Another reason it's so expensive.)
Go to the websites of the agents themselves. Most agencies today have websites and they often have information, even pictures, of the agents, as well as how to submit and what they read.
Look in the acknowledgement page of the books similar to yours or in the same genre. Often writers will thank their agents. Talk to authors you know. It's considered rude to flat out ask an author, especially one you're not friends with, who their agent is. But often an author, even one you don't know, will say who their agent is during a talk at a booksigning, for example. Also, check out the author's website. They sometimes say who their agent is and have a link to the agent's site.
Subscribe to Publishers Lunch online. You'll find out which agents are moving where. In the once a week Lunch Weekly, new sales are listed, along with the agent who repped the book.
Go to or volunteer for conferences where agents are speaking or doing consultations.
And a not-so usual place to research and find agents:
Go to the website for the conference. You don't have to go to the conference itself. Every time you hear in my newsletter Doing It Write or from any other source that a conference is going to have agents attending, go to the website. Most likely, they will have a bio for the agent that will tell not only about the agent and the agency they work for, but also what they or the agency are reading and represent. And this information will be very up-to-date because it's supplied by the agent directly to the organization.
5 weeks ago