Yamaha YAC SN-TV-1SG2R Curved Soprano Saxophone Neck (Yellow Brass w/ Gold Lacquer), Barely Played.
Note that this is labeled as "Curved" but is really just a barely angled neck and is for a straight soprano sax, not a curved soprano sax.
The Yamaha 875 series soprano saxophones come with two necks, but after a lot of comparisons in both a seated and a standing position, I concluded that I have a slight preference for the straight neck, although the curved neck may be a better match for someone who specializes in soprano sax as it has slightly more resistance. They sound almost identical.
As I will never sell my 875EX, I see no point in keeping the extra neck, and it will help fund other woodwind needs. It has only been played for a maximum of thirty minutes (in spurts) during comparison to the straight neck.
You may need to consult Yamaha's site for compatibility info with various soprano saxophone models they make, and of course not all soprano saxes have detachable necks.
These go for $360 new, and are hard to find used so they are usually listed at $275 and almost exclusively from Japan. I am offering free shipping.