JL makes little A available on prime routes like NRT-LHR; it may be as little as 1 A seat per week, so not on every flight and not on every day of the week. They don't want to sell A, they sell F or let the seat fly empty instead, on these routes. No idea if the KVS inventory is accurate, but my past experience with JL is that you won't find many A seats on prime routes, try NRT-SYD or NRT-LAX instead on KVS, there should be A there. If no route ever shows A, then KVS isn't picking up the JL inventory. Also try to find a flight that isn't F0!!!