Bear in mind that both methods -- viewing inventories and looking at seat maps -- have significant shortfalls.

The inventories published by an airline always have a maximum display value. For most US based airlines, you'll never see more than 7 seats in a given inventory bucket at one time. For some Asian carriers, you'll never see more than 4, regardless of how many spots are still available for sale.

The seatmap feature doesn't work because "blocked" seats show up as taken, but also not all passengers have seat assignments. This is especially true if there have been pax re-routed from other flights.