If the game has MT-32 or GM support, you can connect your SC-55ST via the serial port and using SoftMPU. However, this will only work with older real-mode games.
Demo video: https://www.youtube.com/watch?v=p3qCIe0TmtQ

For games that only support FM, it would be possible to write something to output MIDI commands via serial. Not sure how well a Sound Canvas can emulate FM. A Yamaha FB-01 would be ideal as it's based on a FM chip.

Your best bet is a PCMCIA card, but as you say they are rare and not all have hardware FM support in DOS.
PCMCIA Sound Cards

bjt wrote:

If the game has MT-32 or GM support, you can connect your SC-55ST via the serial port and using SoftMPU. However, this will only work with older real-mode games.

Exactly! I have it already, but just wondering if something can redirect or emulate somehow 388h port

It is possible, for real-mode games. But someone has to write it 😀