As you know, most keyboards these days have reasonably good accordion
sounds, but it varies from one keyboard to another. My cheap Radio Shack
keyboard (or one of them anyway) has great accordion sound, but the one with
midi doesn't have that great of an accordion sound although I think there
are at least two accordion sounds available.
I suspect a lot of us have seen or played with various accordions; I've seen button accordions and probably piano accordions at some point; I seem to remember a bit about how both of them look. There are quite a few of us musicians on this list.