This Module is currently available.
3-Channel Linear Mixer
This mixer has three DC-coupled inputs, making it perfect for mixing both audio or CV signals from sources such as VCOs, LFOs and envelopes etc.
Each channel features a unity-gain, linear attenuator.
Features
https://www.wavefonix.com/product-page/3-channel-linear-mixer
These merchants probably sell this module. Huh?