First off, yes, it sucks that Subway won't just sell you their bread on its own. It's good bread, and I really hope that they reconsider.
But to say that the honest answer you got from the manager was "bad customer service?" Sorry, I'm not with you there. These people are working hard for not all that much money, they are not paid to innovate Subway's menu. If there's no button, it's a pretty good indication that what the customer wants just can't be done. That's why it is designed like that.
And was there really a scene at the store? Over some bread? I mean come on, that's a little overboard for some bread, isn't it? I'm trying to imagine a scenario where I would become involved in a "scene" over Subway's bread, and it's just not coming to me.