Several of the big company's have long travel shafts, but they are pricey!
I first had a 4 spline (square) and broke a yoke, and a friend helped me make one out of the heavy PTO stuff you buy at Tractor Supply. Plenty of travel, and so far it's took a beating. Harland, a week at Tellico, URE, The farm in Lincolnton, and Mnt City. It costs about $120 for both inside and out, but it's enough for two maybe three shafts, then you just need the right drive shaft parts and someone to do the machining for you.