I have recently been playing an inherited Chord Organ, with a full set of chord buttons for the left hand and the piano keys for the right hand, however it is not very portable, has a portable version ever been made (besides accordions) like a MIDI keyboard or something with the round chord buttons for the left hand not just the piano keys?
Several arranger keyboards exist in a version with a chromatic button keyboard for the left hand, and also with chromatic button keyboards for both hands. There is e.g. the Orla KX10:
You can also find the Yamaha Tyros range in a version with left-hand chromatic button keyboard:
I'm not 100% sure whether these are factory-made or retro-fits, but there seem to be many of them around on the second-hand market.
There are also chromatic button keyboards that you can place over a piano-style keyboard to convert it, e.g. those sold under the name "Chromaticover":
And there are chromatic MIDI controllers, from the likes of Musictech and Mastermidi:
And then there's the weird and wonderful Chromatone CT-312:
Perhaps a bandoneon would do. They look like a big concertina but their tone is that of a reed organ. The keyboard has an amusing layout.
For flexibility and portability, on of the large button accordions would do. Of course, these are button for both hands. The left hand has a usual 120 bass chord layout along with a three-row bass arrangement. The right hand has a 61-note layout (5-octaves rather than the 2 to 3 in a piano accordion.)
There were several models of “table top” chord organs; I’ve seen them on various used instrument sites, e.g.here or here. Magnus seems like a relevant manufacturer. With these you are usually dealing with non-pristine condition instruments so I’d assume getting one one would require refurbishing it.
However, what really comes to mind is the Suzuki chord guitar if the sound works for you and the cord aspect, as opposed to piano keyboard, is what ypu are going for.
As you're considering Midi; any Midi keyboard can be used as a Chord Organ using the correct software (e.g mainstage on a Mac) - In mainstage, I just add a Chord Trigger midi plugin, and then configure it to the keys I need.