scarcer than hen's teeth

be as scarce as hen's teeth and scarcer than hen's teeth (exceptionally rare; very difficult or impossible to find) — раз два и обчелся; днем с огнем не сыскать;

Example 1: On a rainy night, taxis are as scarce as hen's teeth.

Example 2: It was the President's inauguration and hotel rooms in Washington were as scarce as hen's teeth. (CIDI)

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Since hens have no teeth, this term in effect says that something is so scarce as to be nonexistent. (Answers.com)

see also
[like gold dust]