I don't know if they have any tables larger than 10. Plenty of round six-tops next to each other. Perhaps they will seat you in a cover with two round tables. Did you book as a group?
A Bad Day At Sea [with power] Always Beats A Good Day At Work
Carnival: Glory 2004, Destiny 2008, Splendor 2009, Freedom 2011, Valor 2012, Dream 2013
Celebrity: Summit 2011
Princess: Ruby 2010, 2014, Caribbean 2013, Coral 2014
The largest sitting at a table is 8 on Princess ships.
There are tables for 10 on most of their ships which are oval in shape and not that comfortable if you get stuck at either end. The three people at the ends barely get sufficient room to pull up to the table. Very uncomfortable compared to the round tables.