Im not an industry insider so I dont know for absolute certain, but heres what I have gathered about the whole shebang.
When FASA shut down, major retailers (Amazon, Borders, Barnes and Noble) sold off their remaining warehoused FASA books and then stopped carrying Shadowrun products altogether. FANPRO, being a Germany-based publisher, didn't already have distribution deals with these companies, and these companies did not actively seek out a new distributor for Shadowrun products.
Now that FANPRO is putting out new, revised editions of these books, these retailers have taken notice (either on their own or through requests for SR products) and are starting to stock them again. However, they are only stocking the books put out specifically by FANPRO/Wizkids.
So, while New Seattle is and has been available for some time, none of the major retailers will carry it until the revised version comes out.
If you want it with greater immediacy, you should check out
www.stiggybaby.com.