Wheel bearing at the rear I would think, probably the front CV joint on the front prop?? Front diff, where is the leak?? The seals are all available, the pan is just a bead of instant gasket.
All the bits above are common service items and ready available, a motor factor should be able to order them for you or an online Jeep specialist, they certainly aren't hard to find, don't be tempted by cheap Chinese bits, they are rubbish and don't last.
The transfer box could be expensive, change the oil & see what the old oil looks like, it probably hasn't been done recently...
If you are lucky it may just be transferred noise from the CV joint.
It's worth changing gear oils regularly, they often get forgotten.