Available as an assembled Module and as a DIY project.
This Module is currently available.
Serge Dual Channel Stereo Mixer
DIY panel for Serge Dual Channel Stereo Mixer
http://www.cgs.synth.net/modules/cgs101_dcsm.html
These merchants probably sell this module. Huh?
Included in 85 Racks, 44 are public: