Places in the USA where you might be able to find a “button box” (i.e., Cajun accordion) are –
The Button Box in Massachusetts http://www.buttonbox.com
The House of Musical Traditions in Maryland http://www.hmtrad.com. Those are both on the east coast.
In Michigan there is Elderly Instruments – a great music store http://www.elderly.com. Occasionally Elderly has used accordions in stock.
Castiglione Accordions in Michigan http://www.castiglioneaccordions.com
Mark Savoy – Cheapest Accordions in Louisiana are around $1200US & takes 6-12 weeks to build. www.savoymusiccenter.com
Larry Miller in Louisiana – makes the Bon Tee brand of Cajun Accordions, Rub-boards and Cajun triangles. www.leebenoit.com/boncajun/accordions.htm.
Junior Martin in Louisiana – Accordion builder has a good reputation www.koukous.com/martins.htm
All of the above information courtesy of Garry Kaluzny – http://acs.madonna.edu/~kaluzny/cajun
Washboards— Home of the RU Rhythm Boards, Ray Nutter, West Virginia. Kind enough to airmail a special custom-made sideways washboard for Margot to try out. http://www.amazon.com/Columbus-Washboard-Rhythm-Board-Pine/dp/B0002F4M7K
Earle Bartlett—Maker of Margot’s Rub-board, also maker of Flutes, Bagpipes, Whistles and Bodhrans. Valley Farm, Hartley Vale 2790, New South Wales, Australia. firstname.lastname@example.org
Cajun triangle —
Margot’s Cajun triangle or Tee Fer was made from tempered steel by Larry Miller from a hay-rake in Louisiana. It has curled ends and a leather strap on top to hook over your finger and has what the Cajun’s call a chank-a-chank sound.