Lots of Nigi breeders no longer breed outside does. Diseases being brought into their herd is the primary reason. It may be difficult for you to find anyone to help you there.
Not just Nigerians...goats in general, in my experience. Like a lot of folks, we thought we could probably find a service buck when we first got our does.. But, no... So, like everyone else, we broke down and got a buck.
The irony is that after getting the buck, we balk at the thought of offering him up for outside breedings.
That's just how it works.. When you buy a buck and someone comes looking for an outside breeding from you, you'll say no just like everyone else is saying no to you.