I think it would depend on where you live and whether or not the state/locale laws cover more on the domestic mallard then what the Migratory Bird Treaty of 1918 says.
Here law in Oregon it states:
Sale, Purchase or Exchange of Feathers
Any person may sell, purchase, or exchange lawfully obtained feathers of:
(1) Bird species other than those listed in Appendix 5 (Extant, Self-sustaining Oregon vertebrates by
Physiographic Provinces, Selected Community Types and Selected Habitat Components" of the Oregon Wildlife
Diversity Plan 1993-1998 (November 1993);
(2) Propagated and wild gallinaceous birds, except sharp-tailed grouse (Tympanuchus phasianellus), sage
grouse (Centrocercus urophasianus), and spruce grouse (Dendragapus canadensis):
(3) Migratory waterfowl, for the making of fishing flies, bed pillows and mattresses, and similar commercial
use, provided that such feathers were obtained from birds killed by lawful hunting or seized and condemned by
federal or state game authorities.
And the The Migratory Bird Treaty Act of 1918 would also apply but here are exceptions for non-natives and exotics such as the House Sparrow (Passer domesticus), European Starling (Sturnus vulgaris), Domestic Pigeon or Rock Dove (Columba livia), Monk parakeet (Myiopsitta monachus - the only parrot that doesn't nest in cavities), Eurasian Collared Dove (Streptopelia decaocto), and Canada Goose (Branta canadensis - egg and nest removal without a permit, and hunting), and for some captive-bred birds like mallards.
Disclaimer...I don't know and am not a lawyer or in an way able to actually say one way or another nor am I advising you so please do your own checking.