You can find sponsorship form templates, and lots of other useful templates on the how2fundraise.org site: http://www.how2fundraise.org/fundraising-ideas/generic-tools/
You can edit all of the templates to include details of your fundraising activity.
To access the templates you will need to sign-in. So first time you'll have to register with the site, but registration is free and gives you access to lots of other useful resources.
Good luck with your fundraising,
Donna