If you don't have a current table big enough for your needs and you don't mind the data being crap, try:

create table x as select * from y; -- assuming that y has some rows in it.

insert into x
select * from x;
/

Then just keep pressing '/' to multiply the number of rows in 'x' by two every time.

100000 rows
200000 rows
400000 rows
800000 rows etc....