I looked this one up on the Blogger Help site and they had a few options. Several people have already answered this question and have templates you can download. I won’t go over them here, but I will point you to where you need to go.
NOTE: It bears repeating: Before you mess around with your current template, BACK IT UP. Save it somewhere. Make sure you have a copy of it. You’ll save yourself a ton of frustration.
- New Blogger Template Tutorial: Adding a Second Sidebar
- Templates to download
- Dots Three-Column with Header Template
- New Blogger Three-Column Templates Modified by Ramani
- New Blogger Three-Column Templates by Isnaini
- New Blogger Three-Column Templates by Thur
- Neo Template
- New Blogger Three-Column Templates by Final Sense