I recently saw a post on hear when there was a mum saying she was really struggling to get good quality NAC sweets. I had the same problem but I have found an online sweet shop that specialises in dietary requirements, they do a letterbox No Artificial Colours sweet pack which is just excellent. I hope you see my thread :-) The sweets were really high quality and it was a beautifully packaged item I could have given it as a gift really. Marlows Sweet by post.
I just ordered the small box for my son but they do large one also. Really hope this helps!