Try these 2.
The top one show that your flight was full in coach but seem to have seats available in Business Class.
you just need to know what all the codes are.
Singapore to Bangkok was showing heaps of availability in all classes.
I find the above website helpful if I am wanting to buy Qantas tickets. Qantas gives you your filght price that you chose and then it gives you the cheapest for the day, not much good if all the cheap flights are in the morning and you want to travel at night.