From what I understand, you want to design a device that basically emits some MIDI commands (are you interested in receiving MIDI commands as well? doesn't look like it.)
From the MCU POV, MIDI is very simple. You just need a UART TX @ 31250 bps. (You'll have to choose the system clock properly so that you can get this rate with the embedded UART peripheral of your MCU. This one is pretty easy. 31250 was not choosen randomly. You'll get that from dividing a pretty standard clock rate by a power of two.)
Then it's just a matter of sending a few bytes. MIDI commands/messages are very simple. You really don't need any library to do this. You just need an MCU with an embedded UART, and send bytes.
Actually, MIDI communication is pretty slow, so you could even bit-bang it without any embedded UART peripheral, even on a small MCU (but don't bother, there are craptons of small and cheap MCUs with appropriate UARTs.)