welcome, great to hear you're into fly fishing. You’ll probably be able to find some folks that will swap you some flies for materials.
A couple things that tyers will look for:
-materials need to be bug free
-anything on the skin whether from bird or mammal needs to be cured- not necessarily tanned, salt/borax is OK, but definitely not green or greasy
-there are also some possible complications for stuff like migratory gamebirds (waterfowl for sure and maybe stuff like woodcock?) See part J in this link:
Trading stuff like feathers from other legal game birds like pheasant, turkey is fine, and fur and hair from most other legally taken critters is ok like deer, elk, antelope, coyote, fox, etc (but also check your state's hunting/trapping for restrictions on body parts taken animals even if they are taken legally-- not sure if this applies to any fur/hair/hides but I know some states have rules against possession/trade/sale of stuff like bear gall bladders etc and sale/trade of horns from big horn sheep etc, so there might be on more uncommon stuff in your state even though it might be legal to hunt (wolf, cougar?)
And personal possession of legally taken migratory game bird feathers or skins by anyone for the purpose of tying flies is OK.
But selling or offering for trade feathers or skins from birds covered as migratory game birds is not permitted although they can be given away, and posting an actual offer for trade for these feathers/skins on an internet forum could potentially get you in trouble down the road.
That said, wood duck flank feathers are highly prized by tyers a free gift of some would likely be appreciated with some good kharma at a minimum…
But where direct arrangements for sale/barter of migratory birds are illegal, direct arrangements in return for stuff like pheasant, chukar, and grouse feathers/skins, turkey feathers, and tails, hides with fur or hair from game animals or legally taken furbearers is cool.
What you might also want to do, is to browse through an online fly tying catalog to get a sense of what different stuff is used for, and to get an idea of the going retail prices knowing that realistically you’ll get some what less to have an idea whether it’s even worth the trouble to put it up (some stuff is probably not, some stuff probably is).
Chris Helm, a guy that runs Whitetail Fly Tieing carries a wide range of hides and furs as well as skins and feathers. You can download his catalog from his main page as a PDF -- it would be a good resource for you to get a ball park idea of what's used for what, and to get a sense of the retail value of different bits:
Whitetail Fly Tieing - Chris Helm
And..... the winters are long in Idaho- so now that you’re into fly fishing, think about taking up tying too. It’s cool to catch something on a fly you tied--- but doing it on a fly you tied from an animal you harvested must be even cooler since you’ll have the whole circle of life thing going on.