There are several Internet sites offering feathers for sale including; feathergirl and Taratai Design. This may be an expensive way to purchase them though.
There is also a wholesaler in Papatoetoe called Kentsing Trading Company which supplies the strings of ordinary chicken feathers, natural or dyed. They require washing and drying with a blow dryer to fluff them up.
And there is always parks with ducks and geese where you can pick up feathers.
Don't forget before feathers were used there were hukahuka (tags). It pays not to be fixated on feathers.