You can overcome the RPi scarcity by migrating the code to the Teensy platform, which aside being cheaper and less power hungry than the 2,3,4 RPi, is a lot cheaper and more easily available. Not an easy task since there's no Linux under the hood, but there are some excellent audio/midi libraries to help. They already built commercial-level synthesizers with it. By combining the breath sensor data with other pressure…
I like Teensy but it looks like their boards are either low-inventory or out of stock too: https://www.pjrc.com/store/teensy41.html
And meanwhile the 4.0 is in stock in all SKUs with limit of 20! per person. https://www.pjrc.com/store/teensy40.html
This is pretty available. Especially compared to Pi