A few have bought the zinc plated ones on here but they've given up in just a year, all tarnished. My OEM bolts are still black and fine.. and I quite like them black on the 313's...
You will need M12 x 1.5mm with a 60 degree tapper and i think they are 35mm long. Just check with a rule. Zinc plated wont go rusty. Any black ones can or will go rusty over time. They are black due to a chemical process witch basically impregnates the metal with oil. The better they are done the longer they will last. Dont forget to get 4x for each wheel so 16 + one set of locking wheel nuts.
I would fit wheel spacers at the same time (just a suggestion)
Try the link below Sells bolts and spacers 15mm front 20mm rear (They sell both)with the correct size bolts and locking type.
I have them on Eibach lowered set up and don't have any problems. Car looks great with them on.
I used to have the same issue on my 350z I ended up going for a set of Rays Wheels nuts, they cost me £120 but they were alot lighter then stock and the 3 years I had them they didn't rust at all...baring in mind my zed was a heavily modded car and the wheels were on and off a fair amount
I was impressed with them...not sure if Rays make a set in the required pitch / length but definitely recommend them