All perfect praise be to Allaah, The Lord of the Worlds. I testify that there is none worthy of worship except Allaah, and that Muhammad is His slave and Messenger. We ask Allaah to exalt his mention as well as that of his family and all his companions.
It is not permissible to sell the leather of dead animals before it is tanned as it is impure; purity is a condition for selling an item. This is the view of the majority of the former and late scholars. An-Nawawi said: 'It is not acceptable to sell the leather of dead animals before tanning it according to our school [Shaafi'ee], and this is the view of the majority of the scholars. However, Al-'Abdari reported that Abu Haneefah is of the view that it is permissible.'
Therefore, it is not permissible for you to buy the leather of dead animals slaughtered by non-Muslims, other than the people of the book, before it is tanned, as it takes the ruling of dead animals. Nonetheless, there is no harm to act according to the view of Abu Haneefah who is of the view that it is permissible to buy it in case of necessity as a means of benefiting from it, as you did not find any other alternative than buying it. Even though you do not benefit from it immediately, you will benefit from it in the future. Indeed the necessity makes such a thing permissible as the scholars permitted selling impure dung for necessity.
Allaah Knows best.