The AI007 Quad Eurorack VCA Mixer is available for purchase here: https://aisynthesis.com/product/ai007...

The AI007 Quad VCA Mixer is a compact, high quality, and flexible way to control voltage (audio or cv) in your modular system). Each of the four inputs are DC coupled, allowing the amplitude of CV signals as well as audio rate signals to be voltage controlled. The outputs are also normalled together into a mixer, allowing the AI007 Eurorack Quad VCA Mixer to be used as a voltage controlled mixer. Once a cable is patched into a VCA output that output is removed from the mixer signal, allowing each channel to be used independently, giving users four VCAs in total. A dedicated knob shapes the curve response from Linear to Exponential.

The AI007 Quad VCA Mixer project is advanced and not for beginners. In addition to using SMD parts, (805 and larger,) there are also a large number of thru hold components. Care must be taken to ensure there are no shorts, and if you use additional flux, you may need to probe for continuity in odd places.