First of all, congrats on this massive undertaking! I did the walk in Cleveland last year and am volunteering at it this year, so I know what a huge commitment it is.
I did all of my fundraising online. There was a spot on my teams' website that had pre-written emails that you could customize. I sent them to all my friends (and a few people who I barely knew) and asked them to send it on to anyone they thought would be interested. I also made a point of sending a personal email to everyone who knew my mom. All of the women from her breast cancer support group were happy to contribute. If you have a particular person you are walking in honor/memory of, solicit her friends. After re-reading this, it sounds a little tacky to solicit the friends of dead people, but it really worked well for me (from a fundraising perspective, that is). My mom was a professional fundraiser, so I'm sure she would be proud of me for hitting up her friends.
I know a lot of teams that went to local businesses (like Dairy Queen, etc.) to see what fundraising programs they already had in place. This way, they weren't re-inventing the wheel.
Have you been to any of the meetings the 3-Day sponsors? They usually have a time for people to share fundraising ideas. You can see what others in your area are doing and if it's been successful for them.
Good luck with your fundraising and your walk. Keep your feet healthy and have a fun weekend. Here's some pixie dust for good walking weather!
--Hillary