Hmm.. All of the actions use native integers but for this type of thing it would typically use a long integer which is a different type of variable entirely so custom actions would have to be made for them. I believe they go up to 20, but I can't remember.. Have never really had a need for them.
Beyond that you could make a score builder sort of thing that can compile a string in parts based on smaller multipliers instead of direct score value, I think. There is probably some general info on the net about doing this in unity. Have you looked around on unity answers or the unity forum yet? Might find some high level ideas about it.