As a reference to the event, the idiom "once in a blue moon" means rarely. There is no set amount of time. A blue moon occurs about once every two and a half years. When a single month has two full...
Neither "I gone there once" nor "I been there once" are correct. One would say "I have been there" or "I've been there" OR "I have gone there" or "I've gone there". As for "I was there once" and "I...