Phoenix feathers and qílín horns (see Notes section)
Extremely rare and scarce
Positive
在中国，取得博士学位的人还是凤毛麟角 | Zài zhōngguó, qǔdé bóshì xuéwèi de rén háishì fèngmáolínjiǎo
In China, it's still rare to find someone with a doctorate degree
[Source]
可惜，能够聆听到优秀的演讲的机会凤毛麟角 | Kěxí, nénggòu língtīng dào yōuxiù de yǎnjiǎng de jīhuì fèngmáolínjiǎo
Unfortunately, opportunities to listen to a great speaker are few and far between
[Source]
Few and far between
None
The 麟 (lín) in this chengyu refers to a 麒麟 (qí lín), a mythical Chinese beast. 麒麟 is often translated as "unicorn," but the two mythical creatures have very few similarities
Understanding this story requires understanding that the Chinese word 凤毛 (fèng máo) has a few different meanings. One meaning is "phoenix feathers" (as in feathers from the mythical bird), while its more literary meaning is something along the lines of "a man's talents resemble that of his grandfather."
《世说新语》(Shì Shuō Xīn Yǔ) by southern Sòng Dynasy (南宋, 1127 - 1279) writer 刘义庆 (Liú Yì Qìng). Known in English as "A New Account of the Tales of the World,"《世说新语》is a collection of anecdotes, conversations, and remarks on historic personalities
During the Southern Song Dynasty (南宋, 1127 - 1279), there was a well-known poet named 谢灵运 (Xiè Líng Yùn). 谢灵运 had a grandson named 谢超宗 (Xiè Chāo Zōng) who was also an excellent poet. In fact, he was so great that he worked for 刘子鸾 (Liú Zǐ Luán), the eighth son of the emperor. 刘子鸾 heavily relied on his services, so many of the letters, documents, and other written works that came from 刘子鸾's household were written by 谢超宗 personally.
When 刘子鸾's mother passed away, he ordered 谢超宗 to write her eulogy. The work that the poet produced was beautiful and moving, and even the emperor was deeply impressed. He praised 谢超宗, saying, "You truly take after your grandfather!" (See Notes Section.)
The general 刘道隆 (Liú Dào Lóng) was sitting off to the side when he heard the emperor's words. He was not a man of great learning, and he thought that his monarch was saying that 谢超宗 actually owned rare and valuable phoenix feathers. He was immensely curious as to what they looked like, and so one day, he asked asked 谢超宗 whether he could see them.
The request confused 谢超宗 immensely, and he explained to the general that he was too poor to own such things.
刘道隆 knew that he'd heard the emperor's words clearly, and he grew frustrated at what he thought was an obvious lie. When 谢超宗 continued to claim that he didn't own any phoenix feathers, he simply started searching around the man's house. He searched and searched and searched, but he was never able to find the non-existent phoenix feathers.