As for creating the indexPath object: You can create an indexPath with the
NSIndexPath * indexPath = [NSIndexPath indexPathForRow:itemID inSection:0];
Giving a 0 value to the section index would not matter since, as you point out, there is no section in the carrousel
Finding the index for the itemID, if you use the nicklockwood's iCarousel :
int itemId = [self.myCarroussel currentItemIndex]