Hi Becca!
A guy named Larry Hancock makes some of the best gavels around. He is a super turner, and a really great guy! He wrote up a tutorial for making gavels. Here's the link:
http://www.turnedtreasures.com/pdf_pages/gavel_turning_pdf.pdf
And if you like that, here is the link to his other tutorials:
http://www.turnedtreasures.com/project.html/project_index.html
I hope this helps!
Scott.