Swinger parties are more common than most people think. The swing lifestyle is growing faster than ever.
The common misconception is that swinger parties are all about sex or sex parties as for mentioned in the previous answer.
Swinging or the alternative lifestyle is more about making connections with like minded adults, than the sexual activity that may come with it.
A “swinger” party most commonly is a group that may go out for drinks, dinner, dancing just like any other night out. Maybe some flirting and sexy fun but sex comes last if at all in most cases.
Don’t get us wrong there are parties and events that ‘do’ revolve around the prospect of sex, it’s an even mix and even then it’s not a given.
Too your question, all the time would be the answer.
Depending on your demographic there could be parties and events daily. Taking in to account private meet & greets to house parties which are extremely popular and common. Local clubs in your area may hosts events and or parties weekly or monthly.
The following article that addresses the commonality of swinging and also refers to the popular sites used by swingers nationally. These sites also provide lists of swinger related events in your area which should give you a definitive answer to your question.