Currently, the Capcom Store is the only place you'll find them, and response has been so good that they are running the deal past its original due date until this Thursday night.
So, what's the deal? Order one set, and you'll save four dollars off the regular $39.95 price tag, and get one of their Mega Man Zero buttons with it for free. Order both, and you'll save ten dollars (an extra dollar each), and also get the button.
Source: Capcom Unity