I am sure we are not the only two who have done or are doing this. I have ripped up maybe a dozen vests and jackets and three big sleeping bags that I got from a Goodwill outlet center where everything is sold by the pound. The huge down bag cost $1.28. I almost had tears in my eyes as I crawled out the door, hoping no one was coming for the same bag.
Now I go to the same Goodwill and just paw like everybody else. Sor far a whole bunch of unbelievable good finds (Pelican cases, down quilts, bags galore, Tupperware out the kazoo)
My shop is hometof a bunch of large garbage sacks full of ultrafine down just waiting for a new home. I did leave most of the down in situ cause lots of it is in nice channels (like a king sized quilt that will make a great underquilt)
Good luck and have fun!