Another way to tell is by clicking "details" when selecting a flight.

If one of the booking code options is T (main cabin) or U (business) then it is available at the milesaaver level. This is important because there may be a websaaver that is less than the milesaaver cost, and that doesn't always mean the milesaaver is available.

Example is right now is May 14, LGA-ORD, 6am (AA2911). Both economy and business right now are below milesaaver cost. But there's only milesaaver coach available, not business. You still have to hunt and peck though.