It's not clear to me whether all of your questions have been answered.

The tanned Fox Squirrel hide in the link is indeed what you'll need for the nymph tail. The Dave Whitlock dubbing for the Red Fox Squirrel nymph (nymph and thorax) has the 50% mix of antron and squirrel dubbing called for in the recipe. Nothing to do except use it. It's the main reason I buy the Dave Whitlock dubbing.

Fly tying furs is a good place to shop.

Dave Whitlock, a fellow Okie, is definitely one my favorites.