no they don't have them on their site, but after buying the set up for my GSG5 I was like  this beats anything out there for loading a .22 mag...bar none,
then I got to thinking it wouldn't too insurmountable to make a adapter for the STG mag. every .22 rifle mag has the exact same "feed tower" and feed lip arrangement, so I bought  the one closest one that might fit on the STG mag with modifications, a AR15 conversion adapter.

went to my basement;  because that's  where all the magic happens   and with a file, a coping saw,  piece of wood, screws,  drill and drill bit and good old duct tape and J-B WELD and  super glue I made a adapter to load those 25 round mags


https://www.youtube.com/watch?v=co_qvEKg__4&feature=youtu.be