Can I operate the vehicle in 3 wheel drive since the fixed cam assembly broke?

Hello, In my experience, the front wheel drive does not do anything unless you are off road, but you will have all kinds of traction control/4WD issues if the wheel does not provide resistance to the differential. The other front tire will do nothing, as it has traction, and the one that is disconnected will spin like crazy. If you cannot get the part anywhere else, go to a reputable auto dismantler for the parts. Make sure the warranty is in writing. If you are unsettled by using used parts, consider that the entire rest of the vehicle is made from 17 year old parts. Also, you can contact the shops on this list and see if they can locate the parts: http://repairpal.com/nissan-within-10-miles-of-denver-colorado-80209

Here is a link to replacement auto-locking hubs on EBay. If you want to save money, you could replace with manual hubs for about 1/2 the price. I would not attempt to use the 4WD with only one working hub. http://www.ebay.com/itm/28-Spline-Auto-Wheel-Locking-Hub-For-Nissan-Frontier-Navara-D22-X-Terra-Pickup-/272508155761?hash=item3f72c07771:g:utQAAOSw2xRYaz4a&vxp=mtr