I think of Mosaic as a fruity Simcoe. I love Citra and Amarillo with it, but if those are out I'd still stick with something in the fruity realm if you're looking for other hops to pair it with. Centennial is a good start. Most "C" hops or NZ/Aus hops would be a good match. Galaxy, Cascade, Motueka, Meridian, etc. would all pair nicely in an APA. Columbus, Chinook, Nelson, Simcoe would be nice as well, but to me that takes things in more of an IPAish direction.