This shirt used to be available at a couple of different places but it's since disappeared from those places (I feel like I'm saying "places" too much... places). I've yet to come up with another exact replica, but for one that looks sorta like it (the biggest flaw is that it's missing the background rainbow) try clicking here. For now, it's the best I can do. Hopefully I can update it soon.
Featured on The Big Bang Theory episodes
S08 E09: "The Septum Deviation"
S09 E13: "The Empathy Optimization"
S11, E22: "The Monetary Insufficiency"