The French call it Cul de Becasse.From the same area that you get CDC from a duck but there is much less on a woodcock than on a duck.
I have used it for tying sedge wings but I shoot my own so have never looked into buying it.
I don't have any at present but we don't usually start shooting woodcock until late Nov or Dec then though to the end of Jan.
I have no problem keeping the feathers for you,I don't need paying,would prefer to swap flies if it suited you and is not against the forum rules?
If you PM me your name and address I will send you some when I get some.