Available as an assembled Module and as a DIY project.
This Module is currently available.
Attenuverting Mixer
This is a DC coupled, four channel attenuverting mixer. It is expandable to eight channels.
The board features PC mounted pots, for less wiring and also mounting holes for flexibility. There are Eurorack and MOTM power connecters. It can be built in +/-12V or +/-15V systems without any modifications.
These merchants probably sell this module. Huh?