Will we be able to find a plane ticket to krab on short notice?

i am going to thailand in february. we need to get to krabi but we couldn't buy a cheap ticket through the internet because none of us own a credit card. we will be arriving in bangkok in the late afternoon, my question is, will we be able to find a plane for the next day? and is there a office in the airport suvrnabhumi or something that will sell tickets?