I just went thru this exact scenario last week.
The ONLY place I could find a line for a 1968 was Rockauto..... At almost $200

I got one locally for a 1969 Charger, and all I had to do was change the male fitting in the gear box. Best of all, it was less than $40 ( the flare fitting is larger on a 1969 and up. The threaded port in the box was the same.


edit, added pics