The original and only complete Dallara body kits are apparently still available as an Italian import from one of the established US vendors. The kit in question was designed for racing use only, and is extremely lightweight. It is also prohibitively expensive. Some purchasers have been disappointed with the product. It is probably best to personally examine the kit in which you have interest before buying. The bulky pieces make shipping expensive.
Jason Greenwood offers a choice of Dallara kit, a lightweight for racing, and a heavier, much more sturdy version for street cars. His prices have been reasonable. Customers have been very happy with the product.
http://support.eonsystems.net/scorpionx19/