I have an older Yamaha 211S with the serial number 126001. I haven't found any sites which list serial numbers for Yamaha flutes. Are there any?

You said your flute is always out of tune. I had an Armstrong (US)flute once. It was always out of tune and I was not able to play it with other instruments. Finally I made the shop I had bought it from, send it away to be professionally tested. The embouchure was 3mm out of place. Once this was corrected, it was fine. But I was very upset and the process took years. Eventually I traded it in for a silver yamaha which has been very reliable.

ekdavies: I know of no sites like that. If you contact Yamaha directly, they may well be able to provide you with basic information about your flute.

That's the way, Flutist06.
I've bought a Sankyo flute, and needed to know the year of manufacturing.
I then wrote an email to the factory, in Japan, and they replied not only giving the year, but month and day of fabrication!

Zevang