Unfortunately, no one makes a case or gig bag for the Micro Key 37. I ended up stuffing it in a canvas bag, half sticking out, when I boarded the train.
But for my later train trips and eventual airplane trip home, I needed an actual case for the keyboard.
Then I found a solution. I walked into a local music store in New Jersey and found some gig bags for ukeleles. I measured them -- they were about 25" long; the keyboard is 22" long. Sensing it would work out, I bought one of the ukulele bags ($20) and tried it out. It was a perfect fit!
I ended up buying a Kala concert ukulele bag (Model UB-C). It's even got a pocket, which I store a USB cable in. If you do choose to get one of these as a case, make sure to have the back of the keyboard face the zipper side so as to not damage any keys.

