Publishers (and therefore agents) are very leery of short story collections because, typically, they dont sell. Its kind of a mystery because a lot of people like short stories and a lot of people read short stories, but, for whatever reason, they don’t sell. Publishers will generally only publish short story collections if the author has received some national exposure (i.e. published in the New Yorker, the Atlantic, etc.), has graduated a top tier MFA program (generally Iowa) and/or if the author also has a novel that the publisher loves, and they plan to whet the publics appetite with the short story collection.
Yes, I represent short story collections. But. Rather than pitching your short story collection to an agent, who will likely be reluctant to read your work from the get-go, I would focus on trying to get your stories published. Once you have had some success publishing stories it will be much easier for you to find an agent – one of the best ways to find an agent is to be able to say that you have been published in some very reputable magazines or journals.