Look for agent names in the credits sections of published books that are similar to yours. If the agent was successful with one short story collection, she might be interested in taking on your project.
Consult the "Literary Marketplace" at your local library or search for it online. This will include the names, addresses and phone numbers of agents who might be interested in your collection.
Search sites such as agentquery.com. Record the contact information of each agent that you think would be interested in your book.
Write a strong query letter. The first paragraph of the query letter should contain a hook and outline the direction of your collection. The second paragraph should explain a few of the strongest stories in a sentence or two and the third paragraph should list your publications, awards and any writing education you have received.
Personally address the query letters and send them out according to each agent's conditions. These are always different and can be found on the agent's website.