I see no reason why the method couldn't be mass-produced. The method is to inject the toxin in question into livestock like horses, and to extract the resulting antitoxin. This is the classical method of producing antitoxins, and it is the method still used for the botulin antitoxin that the CDC stockpiles. I see no reason why large quantities of the antitoxin could not be produced in this way. According to the linked story, China seems able to produce adequate quantities. I would imagine it might be possible today to buy large quantities of the antitoxin from China and/or Russia.
I wouldn't say the antitoxin is exactly safe for humans. The chief complication is serum sickness. But I think that a bad reaction is a whole lot better than dying. And the CDC finds the risk acceptable with its botulism antitoxin, which presents precisely the same risk of serum sickness.
For a graphic description of the effectiveness of anthrax antitoxin, read Ken Alibek's Biohazard. In the book, Alibek describes how one of his coworkers was dying of anthrax (cutaneous, but on his neck, so that the swelling was cutting off his breathing,) when he was saved by a timely administration of "antiserum."