To be clear, you are suggesting that if there is interest, you will buy a quantity of these blades and either give them away or pass on at cost to folk at the Moot? Might be better to put that in the Group Buy area.
Personally, I think that 21" is a little short to make into a bucksaw/frame saw. With a bowsaw, you get nearly all the blade length, with a frame saw you lose about 4 inches (0.5" each end with bolts, 1" min for the frame each end, and 1" for your knuckles"). That isn't to say that they might not be great for folk with 21" bowsaws, just as spare blades.
Chris