Where do I find my unique address (URL) for my Seller Store?

From your Seller Dashboard select 'Manage Seller Store', then under 'SEO Friendly URL' will be your address.

Open up your Seller Store by clicking on "View Seller Store" link found on the left side list of your Seller Dashboard. Then, copy the address in the address bar of your browser window and paste that in a separate place where you can find it and store it and share it with others, especially your current mailing list.