Frostweave no doubt has been a bitch to level. Unfortunately I can't aoe down the mobs in Icecrown on my tailor because she is only 76
so I have to use my non-tailor hunter.
I have gotten a decent amount from the Converted Heroes (not the neutral ones) just round the big groups up and aoe. Sometimes I get lucky and get a x4 Frostweave but mostly it is x1.
Another great area is Pit of Saron all the people in the crater at the beginning drop frostweave. I think it is a great drop rate but it is more time consuming.
I still need a ton more frostweave so this will be a while before I can move on and use Embersilk. On my realm a stack of bolts go for 500G (insane) and a stack of 20 fluctuates from 200G to 55G. There have been a few times I picked some up for 38G.. but the majority of the time it is in the 100G range.