Hi, If you're still looking for rust colored yarn, you could try looking at the yarn selection at Hobby Lobby. If there's not one in your area, they have a website. Also, Michael's Arts & Crafts, or a LeeWards.
I would also recommend taking at least part of the project with you to match colors the best you can. You might have to find something "close" and pull out the other rust, and begin again. I've done that with other partially completed projects I've found.