Most of the salmon flies I tie on hooks are in that size range. Mostly I use dyed Chinese cock capes for those. They are available in lots of colours, for not very much money. You should be able to pick them up for no more than $10 a time. While they are not a patch on genetic dry fly hackle, they are ideal for wet flies. If I remember correctly, Wapsi do a range. If you want something a little softer you could look at dyed schlappen. (The feathers behind the saddle from a cockerel). Lots of the classic salmon fly guys use these.
Cheers,
A.