How to tell what model number a Wii nunchuk attachment is?

How to tell what model number a wii nunchuk attachment is?

I just got skyward sword for xmas and really have been wanting to play it. First I found out I needed the Wii motion plus controller and went out and purchased it. I thought all was good and dandy but then it would not pick up my nunchuk attachment. I looked on nintendo website and found that off brand nunchuks don’t work and found that I need a model number RVL-004. I want to make sure before I buy one if it is the right model. Is there anyway to read on the box if it is? are all new ones this number? Thank you for any feedback