The parts catalog at http://www.maxumcustomercare.com/
shows the ladder to be part # 1715851.
You might get lucky and find one at a local Bayliner or Searay dealer. Might have to call around to a few though.
Mine is not the pocket ladder like this but is made by Windline and I have heard other mention Windline is the normal brand used on these.
So check out this Windline 2 step "slide" ladder, could be exactly what you need.
The parts catalog also shows some diagrams on the top so it might just show you what you need. If it does, again, bayliner or searay dealer might be able to locate for you. You can also try Leta's, she has all the canvas patterns and everything for Maxum.