I just got an address for Rheinland-Phalz. This is the administration that paid my friend's father's pension ( ex-german pow who stayed in France )
Landesversicherungsanstalt Rheinland-Phalz.
Eichendorfstrasse 4/6
66720 Speyer, Germany
I don't know if this is the right address for your late dad, but at least you could ask them and they could possibly send you on a track. Hope this helps.

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