I believe you do have to buy the light to get the clip as they aren't available to buy on their own. You can try posting in the marketplace and see if anybody is willing to sell theirs. Still, you have a few other options for getting a pocket clip for your L1D.
The first is to buy a the clip itself. The only place these are available are from knife making supply stores as far as I know. I believe sandwich shoppe also has a clip for sale as well as a fellow forum member. Once you get the clip, you're going to need to drill and tap holes for the clip and its screws.
The only other option I know of is to devise your own means of fixing your L1D to yourself. I chose this option for my L2D. My made a clip out of the a small hose clamp and a tablecloth clamp. The link's in my signature. It's not pretty, but it works.