For the ever-loving life of me I can NOT make out who these specific robots are. There appear to be two of them, however, and they seem to be scattered about evenly all over this shirt (hence the uncreative shirt title). The shirt used to be available at Shirts.comand FiveCrownClothing.com but it's since gone out of stock in the former and has completely vanished without a trace from the latter. Due to this, I've sadly run out of ideas as to where the t-shirt can now be purchased and, ignorant of who these blasted machina are, I'm low on search terms to use to hunt them down. If anyone out there can help shed some light on this t-shirt, be sure to let us know. Until then, it appears we're outta luck.
Featured on The Big Bang Theory episodes
S01 E09: "The Cooper-Hofstadter Polarization"
S02 E08: "The Lizard–Spock Expansion"