
Have just had it pointed out to me :D that I should stress that I don't have personal experience of these breeders' stock, just pointing out that these are the breeders listed who are most 'well known for blue merle collies', as you asked.
As with all puppy buying, you should ensure that you find out what type you like, as mentioned, and most importantly ensure that you are buying from a breeder who health tests.
Is that better? ;)
M.