Hi!
If you dun mind lack of accuracy and only 2 choices of colors, can get either "Jedi" or "Sith" Robe from
Pan-In-The-Box aka
CostumeBase.
Chinatown Point
#02-09
Tel: 90673293 (Hp)
http://stores.ebay.com/costumebases
If you rather have one done according to your personal selection of color, design, as MandalorianBleahhh said, get the prefered cloth from cloth district like Arab Street or People's Park (Food & Shopping Centre) and get a tailor to do it for you.
But if you can sew, you might want to try to make one yourself.
You can either use online tutorial for it OR get a Commercial Pattern for a Robe from Spotlight and modify it slightly to suit your need, and make the robe yourself.
If you just want one for the heck of it, then there is the Rubies Jedi Robe but be warned it's Halloween Quality.
The original cloth used for most of the Jedi Robe was this WWII Blanket. I had touched it before, both the original costumes (OB1 and Anakin) and a sample of it (
from my Deluxe DAG Book), and tho' it looked thick, it's a bit "spongy" and "light".
Not sure where in Singapore can find it but many had used a range of other alternative cloths like Cotton Drill, Suiting, Denin etc. The key here is "thickness", drape and budget.