In addition to ThinkGood's links, here are some more, but they may be used. That doesn't seem to be a problem for your customer, buti"d be leerey about any warranty.
www.bdelectrical.com www.allbreakers.com www.qualityswitchgear.net www.rgindustries.net anyelectric@hotmail.com
www.jrlelectricsupplyinc.com 877-BRKRS4L(ess) [phone]
-OR-
You might try PEARL, [ Professional Electrical Aparatus Recyclers League, and they may be able to direct you to a particular member firm.
www.pearl1.org e-mail: pearl@pearl1.org
I hope it helps.
