I should have guessed this was a train related question.

You might find that process automation components - the sort of things used in factories - will suit your needs. I've seen length adjustable shafts (on splines) with universal joints at both ends before...

There must be many more people who do this sort of stuff but here's one hit I got from google:-

http://www.beldenuniversaljoints.com/?gclid=CJinvfOThakCFUOFDgodTnfHkQ

__________________
1992 W201 190E 1.8 171,000 km - Daily driver
1981 W123 300D ~ 100,000 miles / 160,000 km - project car stripped to the bone
1965 Land Rover Series 2a Station Wagon CIS recovery therapy!
1961 Volvo PV544 Bare metal rat rod-ish thing

I'm here to chat about cars and to help others - I'm not here "to always be right" like an internet warrior



Don't leave that there - I'll take it to bits!