I don't have a set of modern Airborne Regiment collars in my collection, so I'm just going from memory. The main difference is the quality of the construction and the material used. The wartime collars are in silver with a brass overlay and are of very good quality, whereas the modern exampls are white metal and a lesser quality. For reenacting purposes, I'm sure that the Airborne Regiment collars would do just fine. They are not hard to find.
In fact, you can buy them at http://www.joedrouin.com/abe_pins.htm for $6.20 plus shipping and taxes. If you are near Ottawa, Joe is often at the Ottawa Militaria Show which is coming up on April 15.