The most usual place to find - and with some luck, buy - a fixed barrel Falke air rifle, is the german auction site E-gun.
Right now a model 80, No.39 is offered, and I like your attention for what looks like a Weihrauch 77 rear sight attached to it.
Apart from the corroded state and the damaged 'fixed' butt, the absence of the exclusive rearsight to my mind is the major set-back of this offering.
Also, the lever of the loading tap is welded (back) on, now in the form of a bent rod.
Still, I would not be surprised at least someone will meet the starting price of 250 euro.