So it seems that I'm not the only one that said "Oh, wow. Where can I get that dress?" after "A Night at the Bones Museum" aired a couple of weeks ago. Someone wrote into Entertainment Weekly asking the very same questions, and they so nicely hunted down the information.
The dress is the Surplice Chiffon Dress by Adrianna Papell and can be bought at Nordstroms. You can also find the dress that Tamara Taylor (Cam) wore in the episode here. It, too, was designed by Adrianna Papell.
(Thanks to everyone who emailed me about the article!)