For the Grand Rapids, MI walk last year, Jennifer's husbands work donated water, juice, fruit, cookies for the break station and afterwards. We also had an preeclampsia member donate her massage services, baseball tickets from the local team. We also did not have any major sponsors, due to the time restrictions.I would suggest baby store, hospitals, restruants, retail, banks, sports teams.
My best advice is to go out and ask. And go in person--I find this most effective. It is more hard for the company to say no to your face, than to a letter or over the phone.
Hope this helps.