check with your local parks or even the college if you are close. They shouldn't have a problem with you raking up as much as you need.
I grab a couple trash cans full every fall from an apartment complex around the corner from me. I tried to ask permission, but no one spoke english.. so I just get the ones off the sidewalk....they actually blow up against a fence, so I don't even have to rake. My worms love the stuff! (worm bin)
good luck.
Ed

Thanks for sharing the good advice.