Room and Board used to sell bases, not sure if they still do, but think it would be worth a look. In fact one of the pictures in the link looks like a table base they sell.

Here is a potential dining table hubby said the color maybe too dark.

If you need to expand the size of your table several times each year, keep looking for one that both expands as much as you need and that suits your taste. If you entertain even if it is just family several times each year, plan ahead how the table you choose will work -- or how a second table might fit in the room. Another thought: A "heavy" table in a relatively small room has some potential to visually shrink the room. What other pieces (buffet or china cabinet) can make a difference on whether or not any table "works" well, too. If the ends of a pair of tables you choose are the same height and squared, putting two tables together could work.

Are you going to have bar stools? How wide from the outside wall to the island is the area? How does a square table extend to become circular???