NECA is beginning a bold new behavioral experiment, to determine whether the addition of a logo will render plain orange jumpsuits desirable enough for consumers to purchase them in high quantities and for $100 each. The company's hypothesis is that it will, and we tend to agree.
In order to get one of NECA's official Portal 2 Chell Jumpsuits (in women's and men's sizes) from ThinkGeek, you need to get on a mailing list. ThinkGeek will alert its "Test Subjects" about the product's availability when it arrives in October. This is the only way the retailer plans to sell these, so if you want that testy look go sign up now.
Pre-orders are available from a variety of other retailers, some of which have their own restrictions – like only offering reservations during the weekend of Comic-Con (i.e. now). Given the response to other Portal memorabilia, you're better off pre-ordering immediately from your retailer of choice.