Kleenex, flowers, perfume, hair spray, even hand lotion could be suspect because the evidence would be washed away or discarded by the time symptoms appeared.
Notice that both women lived alone so no one would see him if he posed as a salesman and rang their doorbell. Another possibility could be something as simple as a male shopper wandering in a store. Picks up a package of meat, puts in basket, contaminates it with a vial of anthrax. Then he approaches a woman saying he was getting this but now thought maybe it might be bad meat, would she give an opinion? Of course, she would smell it, say no - appears ok and leave. He purchases the product and promptly destroys it destroying the evidence.
Where have all these anthrax spores been floating around?
In countless post offices and the mail.
Somehow, somewhere, the two women got in contact with a piece of infected mail,
perhaps at the hairdresser's, as someone suggested, or a grocery store.
And a 94 year old woman with low resistance probably could be infected with just a few spores
from a magazine that just slightly touched another infected envelope.