I've been looking into this myself - and my local stealer says there is no such touch-up kit for wheels.......there is only paint for body colours.
So i asked my contacts in the paint game to look up Glasurit TitanSilber Met - 9765 and was presented with a book of paint chips to look at.
9765 appeared to be a darker shade of silver than my car (Iridium silver) and didn't seem to have that "high lustre" we're searching for.
I had another of my paint contacts take a quick look at my wheels and he suggested that the high lustre finish is acheived with smaller particles of metallic flake, giving more of a fine sheen effect, which isn't found with body panel paints.
On very close inspection, I could see his point - the flakes of metallic are much finer on the wheels compared to the body, but he couldn't offer any further assistance
So, now im trying to get some answers from paint suppliers and paint tinting specialists.
All formulas for wheel paint shades should be available through Standox as previously mentioned.