I have found one in my old blitzmax folders. It was written by Alan MacDonald way back when blitzmax was fairly new, but I think it might still work. I have used this a few years back for playing mod tunes, so at least it worked back then. I have attached the code. To use it you unpack the folder and copy it to the module folder of blitzmax and then import the module.
[edit] You will need to download the bass.dll from somewhere and put that in the folder of your blitzmax project.