Cadalyst sent me a tips and tricks email with the promise of a link to a lisp file written by Douglas Lernerto export linetypes from a drawing to a LIN file. But, there seems to be a bit of a broken link. I searched their site and came up with a lisp written in 1995 by Greg Oliver. Find it here, or copy paste from below.
; TIP1076.LSP: LLTYPES.LSP Extract Linetypes (c)1995, Greg Oliver