I assume the music must be playing in Alphabetical order? I haven't tried playing songs in Mamewah and though this is not the slick solution you are looking for if it is an aplphabetical thing this will work:
you can make minor modifications to this bat file here:
http://kb.mozillazine.org/index.phtml?title=Random_SplashscreenBasically you would replace "Pic" with "song" and "bmp" with "mp3" in every case and replace "SplashScr" with the name of the directory in which you keep your music.
All your songs in your music directory need to be named 1.mp3 - n.mp3 and what this bat file will do is rename a random mp3 to whatever you want I suggest a,b or c.mp3 and have the bat file put them in whatever directory Mamewah looks for when searching for music.
The same script can be repeated as many times as you want in the same bat file. I use a similar approach to randomly grab one of 4 mpgs and rename them to mameintro.mpg on startup.
Of course all of this assumes you will be using a Mamewah.bat file which will run this script then launch Mamewah so the only time you get a new music sort is when you actually launmch Mamewah. An alternative might be to use a Mame.bat file to launch mame but have it re-sort your music prior to launching Mame so when you exit and return to Mamewah theoretically you will have different songs playing.
So unless someone has a simpler solution this should work for you.