You should be able to get an f 1.4 Nikkor on Ebay for a reasonable price. A 0.9 lens might be located, but you wouldn't like the lack of sharpness.
Like most Nikons, yours has superior high ISO performance, so you'd probably be better off cranking up the ISO to 12800 or so and you'd still get good results. Faster lens will give you two, maybe three stops more light than what you have now, but a higher ISO can give you usable results with five stops improvement over ISO 400. At least your camera will.
I have super fast lenses for my camera, but I really never have to use them.