I guess I am not the only one with wool radar in the thrift stores!!
It's about all I am looking for in there, and I have found some sweet Pendletons, Merino wool sweaters, and nice colors too.
I just walk down the aisles looking for the texture of wool and earth tone plaids.
I have had less luck finding good pants than shirts and sweaters. It is harder to find the right fit, but there are definitely some good wool cargo pants from time to time.
You might still need to buy wool underlayers new...
Good luck