Goose shoulder is one of the easiest marrying and least expensive materials you can use. It is also readily availble. The downside is you can't tie truly large flies (as in larger the #2/0) flies with it because the barbs aren't long enough. For truly large flies, dyed white turkey tail is ideal.
Duck flank feathers are not used as part of a married wing, they are used as sides, throats, tail, tail veilings, or roof on a fly, not an component of the married wing itself. Gadwal is pretty much just used for throats on spey and dee flies. Although it makes for a very nice strip wing on flies like the SILVER BLUE, Teal is prefered because it is lighter and has more contrast than Gadwal as a wing.
You will also need to get some Golden Pheasant center tails, Amhearst Pheasant tails (both center and side tail feathers), Peacock Secondary Wing feathers, Brown Mottled Turkey Tail (i.e. wild turkey tail). and Cinnamon Turkey tail.