I already had 100 grams of reasonable down here from Simon at TierGear and I just bought 30 grams of Eider from a firm in Adelaide as an add-on when I bought a new duvet for the bed.
that total is a bit on the lite side for a winter vest but probably enough in conjunction with my UL jacket.
My first and so far only thought is to buy a big strong and clear plastic bag; add the downs to it and shake like mad but perhaps somebody has a better idea.
About time I made the vest I've been talking about for years and use some of my fabric stash up