I have a new 08 express 3500 lt that came without rear window defroster option. Is there any way to retro fit this option?

 

If this is an option for that vehicle then yes you can.

 

I don't know of any aftermarket kits out there that will just stick to the window. Not saying that there aren't though.
You may end up replacing the window with one that has the grids on it

 

The only way to add rear window defroster is to replace the rear glass with glass that
has the heater grid. You also will need to remove the left rear plastic panel inside the
rear doors, and see if the heavy gauge wire is there. You will still have to find a way to
power the defroster. Not a easy task.