As a living historian and grandson of a WW2 vet as well as some of my living history buddies, we all gather info from a variety of places to ensure our accuracy, some web sites such as www.atthefront.com and www.whatpriceglory.com provides great info and accurate uniforms and equipment.
Another great place is original photos, photos provide excellent minute details most people overlook, for example photos may have soldiers wearing double buckle boots or maybe roughouts with leggings and etc, photos show the uniform and how they wore it. Another place for good info is WW2 Training Manuels, they are great sources for one reason, its the way the guys were taught back then and its what we use now. Another great source of info is the vets themselves, the provide us with the daily ins and outs of a soldiers life during the war.
I usually buy the real uniforms whenever I can and I buy the original equipment whenever possible, it has that history already behind it and the vets seem to know what is real and what is reproduced as far as how it is aged, and I would just assume have the real deal for the vets to look at and handle, some have even put my uniforms on.
Now that all being said there are some groups out there that their stuff isn't authentic nor real, nor does it come close to the real deal, however I have not personally ran across them here locally in my area.
Jason Denno