Was poking around online tonight, and came across this site, sells Tamiya semi axles converted for steering. Sells the conversion by itself as well, but an interesting option if you have to use semi axles on your project.
Link
Not particularly cheeap though, about 95Euro/$130US. Cheaper to buy the Integy aluminium axles.
But i did see they also have extended shafts for 3 speed gearboxes so you can use a front and rear output, no transfer case needed. Same as Joe had but ran out
Shaft
No idea if the shop is any good though. Anyone ordered from them before?