We strongly discourage getting another leaf for a table made after the fact. When a table is built, it’s built with the leaves you order at the time in mind. Consideration is given to the carriage and the maximum length when open (the Amish will not build anything unstable, and adding a leaf after the fact may cause stability issues if it makes the table too big.)
When a table is built and stained, it’s done with all the leaves inside of it. This gives it a consistent stain and fit across the entire top. When adding a leaf after the fact, it may not fit right and the stain/woodgrain difference will be very noticeable with the leaf in.