The purpose of a notary is to ensure that you are really the person that is signing and filing the Oath form.
The county clerk's office can usually notarize your Oath form for a small fee. Another option that may be more convenient is to go to your local bank, they usually have a notary on staff.
Go to County Resources to see contact information for your county clerk.
Does your work schedule make it hard to get to the clerk's office for a notary?
There may be other options to have your petition notarized. A quick google search for a notary in your area should bring up several options. There is also www.notarize.com that can notarize documents over the internet.