My wife and I traveled to Tokyo a couple of years ago to see one of her friends, and I too liked the little boarding tunes. I jokingly mentioned that I would like to have them on CD. To my surprise, my wife's friend said that such a CD existed. So we headed to a CD store and bought "Super Bell Z" by Moter Man (I may be getting the name of the artist and the name of the album mixed up). It was not exactly what I was looking for.
The disc starts out with a recording of the train jingles, which is what I was looking for. But just when you start getting into it, a loud, "Mortal Kombat-style" techno beat kicks in with train announcements played over top. It's quite hilarious.