Since there are only a few days left till your flight, I presume the seat maps are unavailable because the ground staff in AMS now have control over the seats. This usually occurs 48 hours before departure and goes for all airlines.
If you have more than 48 hours before departure then the flight will most likely be almost full. KL (and probably all airlines) blocks seat selection when almost all tickets are sold so they can assign last minute families to seat together.
My advice is to check-in online 32 hours before departure, I expect all seats that were available before the map was locked to be available at check-in.