How would I get a statement notarized?

What do you mean by the interested party? Make sure it's addressed to the right person?

You write it up, but don't sign it. Bring it to a notary, like at any bank. Sign it in front of them, after you show them your ID. Poof. It's notarized.

try your bank most have free notary services for members

Look up "notary" in your phone book, it costs like $5 to get it done.

Take it to your bank/credit union and have them do it. Or, try your insurance agent, a realtor you're familiar with, or someone who advertises the service. If they advertise, they will charge you a nominal fee, but the others will do it gratis.

You must not sign it until you are in front of a certified notary to include all interested parties in the matter which require signature. I am personally hold a notary certification as well and this is the most common issue that will lead to disqualification.

It is common that I will get a document with a signature on it or without an interested party.

Your bank is a great place to start. As indicated they are very economically priced, if is not offered as a free service for its members. Other places that you may want to try are FedEx Kinko's and The UPS Store. These are alternatives to your current bank. They as well are very reasonably priced. There are mobile notaries as well, but are not very economical especially if you are just notarizing a single document. The mobile notaries are more commonly used during real estate transactions.
Make sure that you do not sign the document prior to getting it notarized. The notary will need to verify your signature being made on the document.