For the 14-24, Lee makes a specialized SW-150 filter holder that holds 150mm filters. They also make an adaptor to put the SW holder (and it's filters) on to a normal lens. However they only make a limited number of filters in this size... 0.3 (1 stop), 0.45 (1.5 stop), 0.6 (2 stop), 0.75 (2.5 stop), 0.9 (3 stop) and a graduated ND. They do not offer polarizers or "big stopper" 10 stop ND filters. I don't know if other filter companies make other 150mm filters that would fit.
Just keep in mind these are pretty big filters to be carrying around. There are also some post-processing options available that can do as good or better. Photographing 2 or 3 exposures would let you blend them to create a graduated ND effect (and if you're shooting with a D3/D700 or later full frame camera, the dynamic range is so wide on some of them the RAW files might give you enough in a single shot). If you're trying to do long exposures, photographing several images and then averaging them together can give you a similar result. If you're used to and prefer ND or Grad filters, that's fine just throwing a 2nd option out there if it's too cumbersome.