That is a good question. Not sure about US-based airlines but Korea-based airlines do not really have much of a sale for flights to Korea during the summer time. It is peak travel season and planes are usually fully booked. Having said that, I have searched Kayak.com and they have a Price Trend alert that gives advice on when to buy. For example, I put in MCO-ICN for flights during June and United gives some decent pricing, but the Kayak Price Trend says to wait with an 81% confidence that prices may fall within 7 days.

Or you can use an online site such as Expedia and they have a low price guarantee if another flight shows up cheaper within 24 hours of booking, then you get the price difference.