Is the 50n25pr00 out of production? It's listed as "out of stock" but I can't find it on Tymphany's website.
Out of stock there, too. There's a scalper who wants triple; that's all I can find.
You might try the new balanced-mode drivers. Thing is they are low impedance, so you might want to add resistors to get it to a better level and load.
That's an "off-ear headphone" transducer - it's used in the Valve Index, where it sits next to the ear.
Here's hoping it's just out of stock.