I have seen a low voltage lighting system used in a few commercial locations that I would like to gather more information on.

The lighting system resembles a knob-and-tube wiring system. There are two conductors (sometimes insulated, sometimes not) installed approx. 4" apart in free air. Low voltage heads are connected to and supported by these branch circuit conductors. The secondary of a power transformer supplies the two conductors.

Does anyone know what this lighting system is called. More importantly can you refer me to manufacturers of such. Thanks in advance.

These are usually called cable lights. I recently installed a system and they look great! Cant think of the manufacturer right now but search the web for cable lights and you will find something im sure. If I think of the manufacturer I'll post it here. You may want to knoe that these are a bit of a pain to install.

I dont know where you are located but in the Boston area you could go to Wolfers Lighting and they would help you. Check out their web site www.wolfers.com hit the search button and then click on track and cable lights. They have a huge selection and quite a variety of styles.

Home Depot carries these lights too.

See the National Electrical Code ARTICLE 411 Lighting Systems Operating at 30 Volts or Less
411.1 Scope.
This article covers lighting systems operating at 30 volts or less and their associated components.
411.2 Definition.
Lighting Systems Operating at 30 Volts or Less. A lighting system consisting of an isolating power supply operating at 30 volts (42.4 volts peak) or less, under any load condition, with one or more secondary circuits, each limited to 25 amperes maximum, supplying luminaires (lighting fixtures) and associated equipment identified for the use.
411.3 Listing Required.
Lighting systems operating at 30 volts or less shall be listed for the purpose.