Where can I get an i-9 form for employment?

The employer is supposed to provide the form. It does not have to be notarized, but you need to bring the forms of id specified in the instructions. https://www.uscis.gov/i-9

The I-9 can be found and downloaded by going to IRS.com/forms. The instructions for completing one are also available, but you will need two documents (those are also listed in the instructions) - originals, not copies. It does not have to be notarized.

The I-9 form confirms that you are who you say you are and what is your legal status in this country.

The company should have a stock of blank I-9 forms. You can also get it on the internet. It does not have to be notarized, but you sign it under penalty of perjury. Original means not a photocopy.

You fill out and sign section 1, AFTER accepting the job offer. The employer fills out and sign section 2 and 3.

The form is at https://www.uscis.gov/sites/default/files/files/form/i-9.pdf

It does not have to be notarized.

You are misinterpreting. They didn't mean originals of the forms and they didn't mean that originals were what they want. What they meant is that the laws of the United States of America require you give them originals (and not copies) of your proof of identity and eligibility to work in the U.S. (typically a license to drive or non-driver state ID and a birth certificate).

IRS.gov

The employer provides the form, you must supply your identification in the form of either your drivers license and social security card, or a passport.

Here is the form https://www.uscis.gov/system/files_force/files/form/i-9-paper-version.pdf?download=1

You can only complete the first page the second must be completed by the employer when you are hired.

The third page shows the IDs that you can choose from to take to your employer so they can complete page 2.