Rod: Thanks for the direction, which was fruitful in the form of David Cornell's arrangement for duet that I attach here for anyone else who passes this way: Cornell-Captain-Pugwash.pdf. It is a good practice piece in that it covers the entire range of the Elise. What I uploaded first was a rendering of either a MIDI or ABC from Nigel Gatherer, I can't remember which came first, that I intended to transcribe for penny-whistle.
I am wishing that I took up the concertina years ago instead of faffing about with the piano. Still, better late than never. The resources of the Internet weren't available to help me decide on a system when I first starting thinking about the instrument; the technology is a great boon. I've got as far as Long, Long ago in Wim Wakker's tutor; it is a simple tune that sounds delightful on the concertina whereas it would be a bit boring on the piano. The concertina is a forgiving instrument in contrast to the piano that needs the dexterity of James P. Johnson or Willie Smith to sound any good. And, of course, in terms of portability there is no contest between the concertina and the piano. Have concertina, will travel!
Thanks again for your help.