Our PTO does not run a gift auction, however, I started running a gift auction last year for our local Blind Center. I know we are speaking of two different organizations, but some of the things we found positive:
If you send a letter, and do not recieve a response, follow up with an email or a phone call.
It is alwasy better in person, if possible. Harder to say no to a face.
Sometimes, working the 'poor us' factor is in your favor. I hate to say it, but companies are more apt to donate if you have a higher percentage of disabled/special needs classes. We got that from one of our donators themselves.
Send to EVERYONE! The worst they could say is no, and you just never know who will say yes!
We recieved many tickets/donated items from the least unlikely places.
Local dentists donated teeth whitening, we had an eye Dr. donate lasik, tax preperation, a simple will, we even had a local funeral home donate(a bit morbid, I know) a casket of your choice.
My first year running the auction(there are only two of us who are sighted and did almost all of the solicitation) we raised $6,753. Mind you, there are only about 35 people who belong tho this organization.
Good luck to all of you! Keep up the good work.