Who made Brad Pitt's silver shirt in his first scene in Ocean's 11,
and where/how could I get one the same?

It appears that the clothing worn by Brad Pitt as "Rusty" in "Ocean's
11" was not off-the-rack, but was custom-designed by Jeffrey Kurland
(the film's chief costume designer):

"Kurland began with Danny and Rusty because they initiate the
elaborate caper. 'Danny is more of a solid character ? the
classic-looking guy, the Cary Grant of the movie. There's hardly a
thing that George Clooney can't wear and wear well. While the heist is
Danny's idea, Rusty is the man who makes it happen. So he was very
important and has great personal style. Brad really wants to discover
the character with you. During a series of early fittings, we came up
with a streamlined, sleek effect to his wardrobe. ?Like a racer,' is
how Brad described it."

http://oceans11.warnerbros.com/costumingplayers.html