If the difference is the slide, barrel, recoil spring, and magazine, then it would appear that you could buy a .380 barrel, recoil spring, and magazine, and convert an LC9 to shoot .380, similar to the .22 conversion kits for 1911s, or how you can convert a .40 S&W to shoot 9mm. If there is no difference in the slide other than the markings, then a different slide wouldn't be necessary, but if there is a difference in the two slides (and there may be, in the way the barrel fits) then you'd need a .380 slide as well.
At that point, it may be just about as cheap to buy a LC380... :lol:
At that point, it may be just about as cheap to buy a LC380... :lol: