1. I only see my old friend once in a blue moon.
2. The last time I went on vacation was a blue moon ago.
3. It's rare to find a blue moon rose in a garden.
4. I'll believe it when pigs fly or a blue moon appears.
5. The chance of winning the lottery is like seeing a blue moon.
6. The restaurant only serves their special dish once in a blue moon.
7. The museum only exhibits this ancient artifact once in a blue moon.
8. The company's annual sale only happens once in a blue moon.
9. I like to treat myself to a fancy dinner at a nice restaurant once in a blue moon.
10. The singer only releases a new album once in a blue moon.