From where did you import the new spear?

Probably a problem with UVW. You will have to edit the UVW map in 3dsmax and assign them to the appropriate spear graphic of your texture skin.

Another way to do that is to use the skin of the original model whose spear you took and cut and paste the spear (make sure they're at the original model's spot) on your current model's skin. However, this would not be a good way if there's already another image on your current model on that particular spot.