Examples:

• And once in a blue moon, they do.
• Once in a blue moon, when we need to discuss meats.
• A case like this comes once in a blue moon.
• Such a thing happens once in a blue moon.
• It does me good to do this once in a blue moon.
• Once in a blue moon, you get a student like that.
• It happens once in a blue moon.
• The love that turns into magic once in a blue moon.
• Once in a blue moon, eh?
• The love that transforms in magic, Once in a blue moon.