TR Rose! Kwik-Sew makes jumpsuit / unitard patterns! You can buy them online, or go to a Hancock Fabrics store. To make things easier for you, and other Portal cosplayers, here's a list of possible patterns to chose from. Not all the patterns below will be correct for this (sorry, but I have a test to study for, but I had to procrastinate a little).
2335 - a men's wetsuit, but it has similar lines to a jumpsuit; maybe good for
3052 - I'm using View A, someday, for a Vash cosplay
I hope this helps some people!