I believe that is one of the BMW options
Go see 72 60 0 000 335 on realoem
Go see 72 60 0 000 335 on realoem
Not sure if this is the same mount
http://www.ebay.de/itm/Nachrustsatz-Feuerloscher-BMW-e28-e30/261357838506
These were available for sure on the euro e24s and I am sure for other cars, but I don't know about E9s. If anyone has one or even the bracket to mount to the seat, I really need the eye candy