In the spring all the mallards hanging around lakes and ponds at the city parks in the Lower Mainland (Vancouver area) molt all over. 4-5 years ago I grabbed a couple of large zip lock bags and filled them with primo mallard flank feathers. Put them in the freezer for about a month and them tossed a mothball in each bag for another month. I have a life-time supply of mallard flank in a number of useful colours (tan, brown, olive, green, pink, blue and natural). Took me about 1/2 an hour on beautiful sunny may day to do it.