The closest you may get to a good working Rough Collie in the USA is over at Widdershins. Inquire about pure rough collie or what is called a farmcollie which may have other blood in it but is a no kidding worker.

http://www.widdershins-fc.com/

heritage Farms seems to have good dogs also.

http://www.heritagefarmscollies.com/Heritage_Farms_Collies/Available_Puppies.html

And - if you are considering an import (recommended) then you can check this breeder in Norway.

http://home.online.no/~roeysla/index.cfm

for the most part you will probably find the best Working Rough Collie on some farm out in the middle of nowhere - doing its job and not being heralded on the web.  Those are much harder to find but I will ask some of the people who live out in the middle of nowhere.