I was in a RR once. A pretty big box was mailed around in a circle, and each person took some and added some.
You got a choice of what you wanted most, especially if you were near the beginning of the circle! However, the postage for that was sometimes over $15 because they sent it Priority and it got heavy.
Usually several people "pre-stuffed" it by sending bigger bags of seeds collected from their garden to the originator. We had lots of Ziplocs and measuring spoons in the box, so people could scoop out and label what they wanted most.
I would join one of your "centralized" one if the specialty was something I could grow. Heather in Canada has done one in that style for several years, based on tomatoes and peppers.
If someone offers to run it, and they receive batches of seed big enough to split, I would enjoy contributing labels and 2"x3" Ziplocs. If you get photos, I can print them in color (about the size of a postage stamp!)
Plus, here's a tiny incentive for the organizer: I'll send you a five-piece set of small, stainless measuring spoons:
TAD = = = = = 1/4 tsp
DASH = = = = 1/12 tsp - - - not 1/8 tsp
PINCH = = = 1/16 tsp
SMIDGEN = 1/32 tsp
DROP = = = 1/64 tsp
