Download TerraForm and you can make your own maps.
http://forums.civfanatics.com/showthread.php?t=126921
The world is 80 squares wide by 50 squares high, but you can't really use the first or last two rows or columns.
So the practical limit is about 76 x 46. That's a lot of space to work with if you make one huge continent. Give it a try!