If your going to approach businesses for sponsorship, there are a few things you should do first.
Get approval before you ask. This way your not wasting your or possible sponsor’s time.
You should specify how many posters you are going to want and where they are going to be posted. All over town mean nothing. This defines the market you are targeting.
Define what the event is and how the company would possibly gain from being involved. This doesn’t always have to be a big money maker, sometimes just being part of a community can help.
Last, think about doing a mailing to the membership. That would be a possible distribution of 2000 people in a definable niche. You could fold a larger poster into an envelope and put a letter with it explaining the event and that you would like the member to post the poster at their office, favorite community center, or any bulletin board they feel it is appropriate for. Also highlight the sponsor in the letter. Then you could approach a vendor that would like to advertise to our group to cover the print cost and mailing expense. This method also distributes the posters for you rather than a group of probably less than 5 taking on the task.
As a commercial printer, it is unlikely any printing business would be gained from our group. As I’ve helped on numerous projects in the past. But, electronics groups, ceramic, leather, and hobby stores would have a great opportunity to market to our group. Even Home Depots and Lowes are possible better options.
Good Luck