Yep, theres lots of choices depending on what you have available. If you have any other foxes or mice carrying the fox gene (its cchcch if I remember rightly off the top of my head), depending on what variety they are those will be the best option. Failing that the other option is an outcross to a black tan (which are more readily available) , as long as the black tan isnt carrying any recessive genes all of the babies will be black tans. If you put the babies to each other and one of the bucks back to the lilac fox mother then you will start getting mixed litters of tans and foxes some of which should be black foxes.
I don't have any other foxes or tans... I think. I do have a merle buck, black, with a white belly. I'm not sure if that's a sign of fox, or if that's natural for the merles. My only other buck is a broken brown/grey color. I just got started in breeding and I have a hard time telling what color my mice are, sorry.