You need to get your very own West Marine catalogue so that you can look
at what is available. No WM or Boat US store seems to have what I need
every time, but the catalogue does. You might have to order parts in. I
found a base plate, 9" O.D. with a part number of 361370 and mfg
SP-68914. This plate supports a 2" diamater pole. I think it's made by
Swivl-Eze. The closest match is probably made by Garelick, on page 773
of WM. Its a "stoable table Pedestal" but they are just showing the full
set that consists of the table base, the floor base and the tube. The
whole thing goes for $120. You might get the WM people to check their
supplier catalogues to see what they can order in to match your needs.
You might need to take the table base off the table and take it with you
for the store to look at.