Where can I find refills for the

G-2 (any mm)
Uni-ball Signo Bit 0.18mm

that are any color besides the regular blue,black and red?
(And apparantly Purple for the G-2 lol)

At one time you could find refills for the 0.18 mm bit at JetPens, but I have noticed that lately they don't even carry the full line of bit pens, much less the refills!

You can purchase some of the Pilot refills here.

If you can read Japanese you might try the uniball Japanese web site for the bit refill.

No orange refills for the G2 =(

They go as faras green and purple, past red, blue and black.

I don't the uni-ball site will sell the refills, but it'll tell me which are available....

I should check amazon.co.jp - tho somehow I doubt they'll sell em too :P

I'm not sure if this is what you are looking for, but try this link:
http://www.tokyopenshop.com/uniball-signo-bit-18-p-73.html