Home improvement department store like Lowes, Home Depot or Sears. There is a slight difference between the unit you get from local garage door co. and the big retailers. The difference is the opener 9ft. rail that allows opener to travel back and forth. The garage door co. will install a professional grade opener this means the 9ft. rail is one piece. The retailers sell a rail that comes from factory in pieces so it can fit in a smaller box. The rail that comes in pieces tends to cause problems with opener functions sooner than the openers with a solid rail. Also the pieced rail is not as strong as the solid one.

rails, chain and belt drive openers

There are slight differences in the rails that come on chain and belt drive openers and screw drive rails. The 5 pieces rail that comes with a Liftmaster chain or belt drive opener will last longer than a 4 piece Genie or Liftmaster screw drive rail. The screw drive rail has a long metal screw inside the rail and when they come in pieces that screw is also in pieces and need to be tied together with small metal coupler and every point where the screw separates there is a gap and over time these gaps deteriorate the trolley or carriage that moves along the screw as it turns. And if the opener malfunctions it can bend the rail out of shape. If this happens the rail will handle this kind of torquing better if the rail is solid compared to a 4 pieces rail. If this happens to a Genie screw rail than it pretty much ruins it. They get much louder and effect the travel of the carriage along the rail especially where the screw rails attach to one another. Solid rails are most definitely the best way to go.