That's what Brenda commented about this post.
First, talk to your publisher. Sometimes they will set these up for you. I understand Valor did an amazing launch with five of their authors last night. Or, if they don't usually do this, they might be willing to give it a try, especially if you do a lot of the legwork for them.
If your publisher is not at all interested, then this is when NETWORKING really earns back all the time and energy you've put into it. Hopefully you're part of some writing associations (if you're not, join some). Many of these associations sponsor a yearly conference and have author signings during the event. See if you can get in on that. Then, while there, get to know the other authors. Find who you really click with and those who have books that will complement but not compete with your book.
Talk to all your author friends and get a group of 3 to 5 authors committed to doing a group signing. It helps if one of the authors is established and has a name that pulls people in.
Designate the author with the best verbal/social/business skills to contact bookstores and set up signings. Pick a theme—these signings work best if you can turn them into a party. Have posters and bag stuffers made for the store. Do door prizes, maybe even cookies. (I always bring special treats and small gifts for the bookstore staff.) Brainstorm and come up with some fun ideas.
Then get the word out: blog, facebook and tweet yourself silly.
When it's over, be sure to THANK the bookstore. Then build on your success. If your group of authors can pull in 100 people and sell books to all of them (or most of them) then the bookstore is going to think you're the best thing since sliced bread and they'll love working with you in the future.