Catalyst Game Labs has Shadowrun 2050 now available as a .pdf or you can put your name on the list to get a print copy as soon as they’re released.
From the announcement:
Okay, the teasing and previews are done! You want Shadowrun 2050? It’s here, now available for PDF purchase and print-pre-order in all its full-color glory. Take your Fourth Edition games into Shadowrun’s past and explore the setting that started it all!