just so you know AB negative is the rarest of all bloods (world wide 1 in 200)
It's the least common of the common blood types. There are entire other groups that are considerably rarer than any of the ABO types. All told there are about 28 "major" groups other than the ABO and Rh groups. These include things such as Lutheran, Duffy, Kidd, Langereis, and others I can't remember.
The upshot is that knowing one's ABO and Rh types isn't necessarily sufficient. You always have to cross-match potential donors with potential recipients.
Here's hoping there are enough donors for our guy.