The Only Way to get Shanks is by catching Wolfs in the wild and breeding them in a Wolf Pen. It will give you a permanent passive income of Shanks and other resources if you feed them.
Its a material only used to craft Panther Fodder. Essential to keep up the mood and food in the Panther Pen.
Check out this guide to learn more about Pens and how to tame and breed Wolfs.