AV cables iPad2 vs iPad3
It sounds like you mean 2nd generation iPad vs 3rd generation iPad, both of those models do use the older 30 pin connector.  

3rd generation isn't new tho so maybe you mean iPad MINI...   the mini 2 and mini 3 both use the newer smaller lightning connector.

If it does go from 30pin to lightning tho, apple does have 2 different style of adapters avaialble. Here and here.