A 'Bayan'
Close relative of the Accordion, they were of such cultural significance that they were regarded as highly as any weapon.
In fact they were mass produced & the Stavka ensured there were plenty to go round.
Keeping up morale was the aim.
I am making a supposition that these were to the Russian what a Harmonica was to the average U.S. soldier, or dare I say the Bagpipes to the British (perhaps Mr 43RR could add more on that)
Now the issue is painting them to decide which one will go on it will be a mission on its own
He says the buttons are 0.35mm diameter
I may even graft one on to a figure if possible if I can make straps looking good enough.
What a neat accessory, thanks Mr Raminator, your like a 1/16th "make a wish foundation" with that printer of yours !!
Below photo of mr Vandra's ZIK-20 
