I'm surprised you're having to use anecdotal information about the number of days of blood supply available in the USA, Brad. After a bit of Googling I found this webpage by some organisation called "America's Blood Centers" which supplies half of the USA's volunteer donor blood.
It looks like there could be some US blood centres that have only 1 day supply or less, and a few more that have only 2 days supply. The colour coding system used for the supply situation at the blood centres, which specifies green for 3 days or more supply, suggests that 3 days supply is regarded as acceptable.
If there was a disaster, I would imagine it wouldn't be difficult to get a lot of blood donors to come forward at short notice.
Silly me, didn't think they would be advertising. Yet the first one on the list (Ohio) shows almost no O- blood. O- is relatively rare, but it is on the edge of not being there. On the same page of query, I saw 3 postings for "critical levels" dated today.
It is nice to know that my blood type seems to be relatively available though. I guess I shouldn't fret too much.