Customer service at Boker USA may be able to help. They are still making that pattern, so it is possible the new pens blades will fit.
If not, I could hook you up with some knife mechanics who might sell you a pen blade, or replace it for you.
As for how easy it is to take one apart and put it back together, I refer back to the old quote "Everything is easy, once you know how!"
It is not difficult to disassemble an old pocketknife. But there are a few tips and tricks that certainly make it easier.
Do a quick google search on knife repair and it will lead you to discussion forums and "how-to" pages.