It seems like DM 500s, 7000 and 7020 have the same tuner :

DBS-Tuner:
Frequency Range 950 …. 2150 MHz
Signal Level - 65 dBm …. - 25 dBm
Signal-to-Noise Level 12 dB max.
DBS-Tuner Input Connector F-Type female
Input Impedance 75 Ohm
AFC +/- 3 MHz
Demodulation Shaped QPSK
FEC Viterbi and Reed-Solomon
Viterbirate 1/2, 2/3, 3/4, 5/6, 7/8, automatic assimilation
Roll-off Factor 35 %
Demultiplexing according ISO 13818-1

Is there anyone who knows where to buy the tuner as sparepart ?