I don't know if this will help :- https://hmi.homewood.net/bellows/ and this one (which refers back to previous. . .) https://www.concertina.net/topic/16630-building-an-eco-concertina/ I hope you can make sense of the above - plenty of pictures in the first one and it goes onto a second "page". Woodworking skills a definite advantage. . .and it seems they have reeds and other metal hardware lurking inside.
Life's too short, eat dessert first! [Source of quote unknown]
You have to be warped to weave [ditto!]
Thank you for the diversion - I am down the rabbit hole again. . .
Should be the sound of a "squeezebox" simple concertina in this site. Used for sea shanties and folk songs apparently.
https://www.dartmoorlife.org.uk/the-squeeze-box-dartmoor-folk-music-audio-guide/ and I found templates for folding the bellows, but it was for paper construction. I'll keep looking.
Life's too short, eat dessert first! [Source of quote unknown]
You have to be warped to weave [ditto!]