If the agent can't give you the information, find one who will. Aside from common-decency reasons, just about the worst way to buy a plane ticket is to call an airline directly and assume the reservations clerk will tell you the best deals in the marketplace. It won't happen. Your agent also can research fares offered by consolidators, which buy large blocks of tickets from major airlines and then sell them at a discount. The guide, available at bookstores, lists consolidators by state and verses consumers on the drawbacks and advantages of buying from a discounter.
Charter flights are another alternative.
These flights offer substantial savings. However, if the flight doesn't go, or there's some delay, you're probably flat out of luck. By traveling before or after the peak months of June, July and August, you'll get a better fare. So buy as early as you can. Last year, airlines reported load factors of 85 percent or better for June and July, with many flights sold out well in advance.