>> Shaking them in a bag may be the way to go, but I'll end up with a sprained arm before I get enough separated to trade
I've never tried to clean fluffy seeds, but I use a version of this a lot with pods and seed heads. I have rigid plastic tubs that used to hold peanut butter or peanuts. The hard sides and good grip let me shake them HARD. (I also use them for seed storage, hence the photo below.) Paper bags drive me crazy because seeds hide in the flaps and crevices.
P.S. While I was briefly serving as a clearing-house for saved seeds to be given away, many people sent bags of fluff with seeds embedded. I always just put a big pinch of fluff into 2"x3" Zip-Locs for sharing.
Then I told myself that the fluffy tails would give people "handles" for sowing each seed individually. I if they planted in rows, the fluff would serve as markers to show the seeds' spacing in the rows.
