Takes time but you can still find them in the shelves of AD. I got mine new from AD last year. It is still available although it has been discontinued since 2007/08. The watch, reference 2254 is available with either the Speedy or Bond type bracelet.
The 50th Anniversary model is the GMT version, reference 2234. I could be wrong but the white dial version of the Seamaster GMT does not have the '50 Years' on the case back. Only the black version has the engraving.