Hi,
The SABRE Platform is being discontinued, which may explain why you can't access the files. Depending on your needs you can use the SABRE Board files.
The Platform and Board are the same PCB, just a different BOM / build option, with the Platform being a fully populated more expensive solution, the Board is a smaller BOM and cheaper overall solution.
You can access the Quad SABRE Board files here -
i.MX 6Quad SABRE Development Board|NXP
Again this is the same PCB as used on the Dual versions. AFAIK an updated Dual SABRE Board is being created to replace the Dual SABRE Platform, but that will not be available until early next year.
Regards
Ross