putnam rolling ladder is a good source. the rail should not be that difficult to install but requires the proper support in the wall or cab.

MWE makes modern sliding ladders like this one with a ton of different options. This looks like it could use one of their handy hook fittings which allows not only to switch from one rail to the next but you can also stow it in the vertical position in a separate spot for when you want it out of the way. You can find all sorts of solutions with rungs and steps here : http://www.betterbuildinghardware.com/collections/library-ladders

You can also install curved rails with a Rolling Library Ladder that can store vertically against the existing cabinets or be removed and stored on another wall. The curved rails will enable the ladder to go all the way along the length of your two walls without being removed from the track. Custom Service Hardware also offers rolling hook ladders which both roll and can be removed from the track at any time. See what we offer here http://www.cshardware.com/rolling-library-ladder

CSH Team