I don't know how long you will have but if you are able to get downtown to Charlotte Yarn Remi is amazing and I adore her. I think Cottage Yarn would be closest to where you will be, but I have never been there
so I can't comment on that one. Rainy Day in Pineville is great & they have spinning supplies. Baskets of Yarn is also nice but she might be a little more of a pain to get to. Same with YarnHouse.
Cottage yarn is great (and closest). My favorite is Yarnhouse on N. Davidson. Baskets of Yarn has a lot of the brands I love like Malabrigo, etc. All are easy to get to from Matthews.