Those vehicles are not in Germany. They are czech-owned and apparently a remaining stock from when Sweden bought ex-East-German BMP1 from Germany and had them modified by a czech company.Curiously however...
Germany okays sale of former GDR infantry fighting vehicles to Ukraine
Germany has approved the delivery to Ukraine of several dozen infantry fighting vehicles (IFVs) that originally belonged to the former communist East Germany amid criticism that Berlin is not sending enough military aid to Kyiv.www.reuters.com
The official statement is that all own Marder IFVs are bound by NATO obligations. All owned Marders are part of active or reserve units, with possible a low maintenance reserve beyond that.I find it a bit hard to believe there isn't a single marder available in NATO.
Particularly as they were supposed to be replaced by the Puma.
There are no disused stocks. Vehicles no longer used are typically sold off to "Battle Tank Dismantling GmbH" (owned by KMW since 2016) and are awaiting disposal with that company in Rockensußra, East Germany. Typically around 500-800 armoured vehicles per year.