Where can I find suitable replacement tubes for Volksempfänger and radios from the Second World War era?

For Volksempfänger and similar radios from the Second World War era, suitable and carefully selected replacement tubes are especially important. This concerns devices such as VE301, VE301 Dyn, DKE38, Olympia-Koffer or similar receivers from this period. Typical tubes include RGN1064, RES164, VCL11 and V301, as well as A-series tubes such as AF3, ABC1, AL4, AK2, AZ1 or UCL11. In the VE301 Dyn, for example, AF7, RES164 and RGN1064 are documented; in the DKE38, among others, VCL11. Anyone who wants to preserve or restore such devices should pay attention to the tube configuration suitable for the respective model and to replacing the capacitors.