The bare PCBs can be ordered from OSH Park here:
https://oshpark.com/shared_projects/jwa4E5lhI don't have a parts list at hand but the connectors are a common Molex part. Email me if more info is needed.
There are a lot of easy reconfigurations that could be accomplished by adding or removing the resistors and making minor programming changes. It should be possible to decode any of the MIDI console status output messages shown in the HW User Guide beginning on page 222.
The voltage regulator is for 3.3v (C33CV) and the driver IC is the ULN2803N.EDIT: Note that the price shown of about $28 is for a set of three boards. That works out to roughly $50 each assembly including the Teensy 3.6, PCB, and the parts. A similar organ encoder/decoder board with 4 SPI connections, 8 general purpose drivers, and 8 pot inputs is in the works subject to a little testing. This will be for the hardware as I'm not sure how the actual programming will progress.