I'm afraid of a bioterrorist anthrax attack, is there a publicly available vaccine?

Vaccine available. A vaccine is available and you should consult your doctor to determine need for it and your suitability as a recipient. Please note that you are more likely to get hit by lightening than get anthrax from a terrorist attack.
Biothrax. Biothrax is an fda approved anthrax vaccine & it is primarily for at risk individuals such as veterinarians, farmers & researchers working with animals. It is also used by military deploying to areas where it could be used in weaponized forms.
Not yet available. Anthrax is a bacterial infection which can be weaponized. Currently the vaccine is only available to the military. It is treated with ciprofloxacin, an antibiotic. The us government. Has a stockpile of Cipro 'just in case'. The biggest, but still very rare, antrhax threat to civilians is from drums made of animal hides (esp. Goats) in other countries. The usda & cdc websites have info about this.