I hate to tell you this, but Chevy never produced a '68 2-dr wagon. It had to be a custom fabrication job. The last 2-dr wagon was in '60. It's too bad, it would have been a cool wagon. After '60, it was the '64-'65 Chevelle 300 series 2-dr wagons.
Longroof is correct, 64 and 65 were the last 300 series 2 dr Chevelle wagons GM made. Unlike the 2dr Sedan Delivery models, some information I have read indicated the earlier 55,56,57 2dr full size Luxury Nomads were not as well received by the publics as the 4 dr models. GM brought back the 2dr Wagon in some Chevelle 300 series models in 64 and 65. Like the earlier full size versions they were also very low in sales and popularity at the time. Of course now we all know better and have created a unique desire for these 2dr models. Unfortunately for me my favorite Chevelle is 1966 and did not have a 2dr Wagon so I designed my own. http://www.stationwagonforums.com/forums/showthread.php?t=29015&highlight=rmay ElCamino's were built on a Station Wagon platform so the right donor parts could be available to do a 68 Chevelle 2dr Wagon conversion. If you come across any photos of the 68, pass them along I would be interested in seeing their design.