I guess you will need to put all the paths to the different folders in an array so that they can be called upon randomly.
Then each of the files in a folder needs to be put in an array and the contents of that array need to be ordered. And since it appears your using numbers as the text file name you can just call the sort() method. Put this code in a frame and preview it with ctrl+enter and look in the output you will get.
List = Array("3", "6", "1", "99", "2");
trace(List.toString());
trace("--------------------")
trace("IN ORDER ::: " + List.sort());