Available as an assembled Module and as a DIY project.
This Module is currently available.
Dual Mono > Stereo
ADDAC219OUT was designed to replace bulky 1/4 inch cables when plugging external stereo gear to the modular realm.
It merges 2 TS mono signals (Left + Right) into a TRS stereo output while also converts the synth inputs to line level.
There's 3 independent sections allowing for three stereo sources to be connected.
https://www.addacsystem.com/en/products/modules/addac200-series/addac219out
These merchants probably sell this module. Huh?