I'm a little confused...do you have that backwards?Are you only looking for the housing, or the entire lower with pack? If you're looking for the complete pack, you'd better try and find one that has not yet been clipped and pinned.
A clipped and pinned factory lower without a registered sear is an illegal machine gun conversion device. And in recent rulings, they've even said that a sear-ready pack, even without the sear, is a no-no.
Clipping and Pinning are modifications to allow you to stay within the laws/regulations. How can a c/p'd lower without a registered sear be considered an illegal machine gun device?
As far as an Sp89/Mp5k conversion... How does one legally use a 4position mp5k lower? Acquire a 4position clipped and pinned lower and swap in the Sp89 internals along with an mp5k selector/axle? Am I thinking along the correct lines here?