If you are patient, you can get them for under US$40 on ebay. Look for both sides of the tube (left and right channels) to be as close to each other as possible. Look for tube meter test readings in the description (don't settle for mere descriptions like "look and sound great!", only buy if there are test readings for both sides of the tube). Of course, look for sellers with good feedback.
See my long post in this thread at:
for a description of the sound difference between ribbed and smooth plate Telefunkens.
BTW, "NOS" means New Old Stock which means a tube that has never been used, and that is actually rare and expensive, and unnecessary, since a good used Telefunken can provide years of good service. I prefer "Vintage" as a term for tubes that were not made in 2012.
You are right "Vintage" is definitely the right term.
By the way, while I have lots of experience with a variety of speaker amps, and have used headphones for years with receivers and pro gear, I have only used a couple of specialized headphone amplifiers - the Bellari and a CmoyBB. So, I decided to try the new Schiit Magni US$100 solid state headphone amplifier. Schiit makes exclusively headphone amps and DACs, and are well regarded (with lots of high-end audio experience). Hearing the Magni with my Shure 1840 and HiFiMan 400 headphones would give me a good, modern reference point. (And of course, if they were better than the Bellari, then I would keep the Magni.)
Overall, I found that the Magni had some good qualities, it was relatively detailed - especially for a US$100 amp. However, I found it to also be somewhat "congested" and had a slight very fine grittiness at times to the sound. In contrast, the Bellari is always very smooth and clear. In addition, with the HE-400, the Magni has insufficient quantity of bass - something that requires the HE-400's excellent bass performance to bring out. (Another reviewer of the Magni has also commented about this.)
I ended up using Schiit's 15-day return policy, but it was interesting to finally compare the Bellari directly to another high quality desktop headphone amplifier - it gives me more confidence that the Bellari is indeed a good choice in its price class.
I've read you're posts on the HE-400 thread. I have no experience with the Schiit Amps/DAC's but the number of positive posts on Magni did interest me. Nice to see a review comparing the Bellari And Magni. Lately I've been building up my computer audio starting with a more portable DAC/Amp the Audioquest Dragonfly playing this off the MBAir at the office with Senns 595. At home I use MBAir>DF>Bellari>HE-400. My last addition was Amarra as software playback off the computer. I did a free demo X 2 weeks and was impressed with the expansion in sound and sequencing with the DF via iTunes.