This will have to be looked at in person to be authenticated and valued. The Museum is correct about that. This cannot be done online. You need to find an appraiser in your area, you need a antique stoneware expert. You can go to the site of International Society of Appraisers and American Society of Appraisers. You can locate one that is an expert in this type of item. Also check locally there are a lot of appraisers in the Florida area.
That is fine. As an appraiser I had to be honest with you and tell you this could not be appraised online, since it cannot be looked at in person or possibly needing to be tested to determine age. This could be a valuable relic and trying to get a value on line, someone giving you a value would be a disservice to you.
You have to contact customer service. You do so by clicking the red flag at the top of the page.