Seems like replying to a post was a short lived luxury...
This kinda sounds like where our pack was 2 years ago... no adults stepping up to help out with things. Kids just randomly not showing up with no communication from their parents.
I'm sorry you are having such poor turnouts for your meetings. I understand that frustration very well indeed. And the kicker is... if you go easy on the planning for Cub Academy, then people will not mind having missed it because it wasn't that great anyway and if you go all out and do a good job, then that's just rewarding the parents for not helping out once again because it went good for the boys without their help (again). It's kind of a No-Win situation!
Maybe you could set up the Cub Academy in such a fashion that it's a "self-serve buffet" type of thing... for example, the boy and his parent could go into a room for the Art Belt Loop and there will be a list of 3 things that need to be accomplished and some supplies and he will have to prove it to his den leader that he finished those 3 things and then they would go into the room for the math belt loop where they find a list of 3 things that need done including a form that they can take home to fill out over the course of the week (or two- since I can't recall from memory what that requirement was) and then once that's done they show the den leader who marks them as having completed it. Then when parents complain, just say this was the best that could happen with NO volunteers!