Per the FAA, SMGCS charts, "are available from private sources (ie: third party charting providers) outside of the FAA." Typically the airport contracts with a particular chart provider to create the SMGCS charts.
Low visibility/SMGCS taxiway or airport diagrams are not currently available within ForeFlight Mobile.
If you obtain a PDF copy of a low visibility/SMGCS taxiway or airport diagram, you can import it into ForeFlight Mobile using the BYOP (bring-your-own-procedures) feature that lets you add PDF copies of procedures to airports. Please view our BYOP page for full instructions on how to use this feature.