Welcome to the forum.
I think it might be helpful if you could elaborate on your questions a bit. By "missing type" do you mean a type of keris from mojopahit that has never been seen. Other's might know more about this but it is not a story i have heard up til now.
As for spears (tombak) they are often mounted in dagger style dress instead of on spear shafts and i have seen spears mounted in keris dress, though it is my understanding that that would be the incorrect way to dress a tombak. Is that what you mean or do you mean are keris ever mounted on spear shafts to be used as spears. That i have not seen.