Spice Simulation Models?
Usually if I need a model that's not in LTSpice, I go onto the manufacturers website (LM means National Semiconductor so you would try there in this case) and type the part number in then look under tools/models on the part's page.
Here's a random example for the LM7732.  

If that doesn't work then google "spice [part number]" often turns something up.  

For the LM317, the first technique didn't work, but google turned a TI model up, linked to in one of the posts on this page.