@George
If you have the L138 you might try a G40 lamp.
There is a thread where someone tested the G40 against the real Durst bulb, and it matched fairly well. And best of all they are easily available, and very inexpensive compared to the Durst/Thorn bulbs.
I plan to use a 60 or 100w G30 in my L1000, once I get it setup.