I'm pretty sure they sold this separately in the Adventurer. I might have an issue sitting in an old game box that has the item number for the pen.
Then you may be able to bug someone working the store at LucasArts to go track down a pen inside whatever warehouse or storage closet they are keeping the remaining unsold pens in and send you one. This is assuming that people who work the LucasArts store enjoy being helpful. Being nice to customer service people on other internet stores over the web to beg them to find something no longer sold or out of stock has worked in a few instances for me.
Of course, it's also possible that Sean Clark left LucasArts with all remaining pens so he could go home and shove them up his ass in the kitchen.