I would suggest some followup phone calls to the businesses that haven't sent you anything yet. Maybe your letter got buried on the owner's desk and they just need a gentle reminder of your request. Or, if you have willing volunteers, they could go in person to local businesses, ask to speak to the owner/manager and ask for the donation in person.
I would also check with the office staff to see where they would put any mail that would have come with donations in it. Maybe there is a whole pile of stuff just waiting for you! At our school office, we have a separate Home and School Association mail slot where our incoming mail is put and I also plan on bringing a tote to leave in the office for any packages that are sent to us for our auction.
When you ask for donations from local businesses, do you have the businesses send their donations to the donation chair's home or to the school? We had asked that businesses send their donations to the school, but it has taken the office about 3 weeks to make us up a mailbox and so far nothing has been received. We sent out the letters about a week ago and gave the businesses a deadline of the first weekend of October to send something in.
Does collecting donations usually take this long? Do businesses usually send their stuff near the end of the due date? Or is someone in the office keeping our stuff? I know that's highly unlikely but I am getting paranoid that we will not be able to pull off our fundraiser due to a lack of funds.