I'm responding to this old post so that maybe I can help someone who also went through this. My Montille (Serial #26) came with Mullard branded tubes, but the codes indicated that they weren't Mullard at all. They turned out to be older IE (Yugo) tubes rebranded as Mullard. At least one other person has told me that his Montille came from the factory with those Yugo tubes as well. They aren't much easier to find compared to old Mullards but once i did locate them they turned out to be great sounding. What didn't sound great were the new driver tubes. I bought Phillips but they just didn't sound as good as the old pair. Now I see they have different colored ink. The original tubes were newer production, compared to the older green inked version. Thats the next experiment. Stay tuned.
Hope this helps someone.