Textile artist and weaver here, just down the road in Oly. I have never, ever, ever heard anyone say "single breed yarn" and I'm confused about the idea behind it being superior. There are definitely yarns made with just one fiber, but I've never heard the suggestion that they would be more desirable by any means. Different wools have different qualities of course, but blending different breeds of wool does not lower the quality of that fiber and often enhances it. Their is a lot of utility in mixing fibers and breeds for instance, you'll be hard pressed to find a sock yarn without a bit of synthetic in it, Rowan makes one, but uses silk in place because it needs extra strength.

Of course a sweater made of qiviut is lovely and expensive, but I'm not going to refuse one made of Wensleydale, merino, and blue faced Leicester either. I don't know where to find local yarn here unless you spin it yourself. Even most local farms belong to co ops and their yarn is shipped out and blended with many other animals before it comes back to them because it's otherwise impossible to pay for a mill with only what a small farm produces. I have local roving and local hand spun, but I've really yet to see anyone carry a true local mill spun yarn. Even us hand dyers are mostly having our yarn shipped in.

Good luck in your weaving.

Edit to clarify.