Available as an assembled Module and as a DIY project.
No info about availability.
Simple, easy to build audio Mixer for Polivoks VCO1, VCO2 and Modulator or any modular setup.
Comes as cost-effective DIY kit.
http://www.ericasynths.lv/en/shop/2935-erica_synths_mixer_diy_kit.html
These merchants probably sell this module. Huh?
Erica Synths Polivoks Mixer V1
Erica Synths DIY Polivoks Mixer