Hi House,
Never seen a finished one without it. Perhaps it was made from a kit? You should be able to get those directly from Traditions if you want it to match the pictures, but you can certainly get different styles of patchboxes from a number of different suppliers, Track of the Wolf being one good source.
If you are going to install a patchbox and the stock is not already inlet to do so, be aware that inletting a pierced patchbox such as come standard on the Shenandoah is a lot more work than inletting one that isn't pierced (pierced patchboxes have sections of wood "piercing" through the brass). If you're trying to pass off the rifle as something that would have been used in the Rev War, go with a standard (non-pierced) patchbox and forgo the star on the forearm of the stock. Both the pierced patchbox and the decorated forearms made their appearance in long rifles after the Rev War in the Golden Age period (1790's to about 1820).
If you're not concerned about that and just like the looks (it does look good!), then you should be able to get the original parts directly from Traditions. It may take quite a while to get them as the parts come from Europe, but I've found them to be pretty helpful in the past myself.
Twisted_1in66 :thumbsup: