What does "SRAM Custom" (front derailleur) mean?
If you look closely at the zoomed photo on Specialized's site, you can see that the label on the "custom" front derailleur says only "SRAM" and "2x10".  The regular ones made by SRAM say "X0" or other model names on them, e.g. here: http://www.competitivecyclist.com/sram-x0-2x10-high-direct-mount-front-derailleur-srm0437

It appears that the style of mount is readily available, but perhaps not the precise model with no labeling that Specialized is using.  Maybe that means they're using something "between" the regular SRAM grades, or maybe a different surface finish, or....  But this shouldn't matter if you simply need to buy a replacement.