How to ask for sponsorships?

I have been asked by my company to get sponsorships /donations, gift cards, gift certificates from local companies around town for an annual conference my company attends. The reason for the donations is for a gift basket for a silent auction at the conference and the money raised goes into our organization which is a local no for profit company in economic development. I have no idea how to do this, every letter i have drafted i think sounds dumb. Does anyone have any sample letters to help me out? So pretty much I want to tell them who we are, what we do we are seeking , gift cards, gift certificates , as well i will be asking some of the local hotels for a two night stay at a discount or as a gift certificate, for this silent auction and hope really heard they help haha. Thank you
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Maybe you should go without the letters, and go in person, look professional, and add a more personal approach. That way you can be sure they at least hear what you're about instead of just discarding the letter.
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