How to start a community sale?

I want to start a community garage sale for my subdivision this year and I plan to make a flyer to let my neighbors know about it, Instead of going door to door handing out a flyer could I ask my mailman to put the flyers in everyones mail box? Is that allowed??

We have locked mailboxes all together and everyday when mailman comes by he has them all open, i dont see why he wouldnt be able to do that..? what do you think? I also considered just making a sign and placing it around there but idk