Any dynamic mic should work. I have seen accordionists use Sm57s in the past. The instrument is quite loud, and occupies a wide swath of the spectrum. Some folks opt for two microphones - one on each side of the accordian. Some companies sell clip on mics for accordians, but I imagine these are more for convenient movement than for good sound. Some accordian players will put piezo transducers inside the accordian itself. These often go under the bass mechanism, and the grill. Just my opinion, but this probably won't sound as good as a dynamic placed outside the microphone.

Any dynamic mic should work. I have seen accordionists use Sm57s in the past. The instrument is quite loud, and occupies a wide swath of the spectrum. Some folks opt for two microphones - one on each side of the accordian. Some companies sell clip on mics for accordians, but I imagine these are more for convenient movement than for good sound. Some accordian players will put piezo transducers inside the accordian itself. These often go under the bass mechanism, and the grill. Just my opinion, but this probably won't sound as good as a dynamic placed outside the instrument.