This site supplies you with a program that lets you
create graph paper however it only works for a high
resolution screen setting. It is not too helpful if your screen’s resolution is too low.
I recommend this site as the best. I don't think it has
anything in the range of mm I think it is in inches
but it does have cm squares and some others too.
This is another graph-printing program. I didn't have
time to check it out extensively. Let me know if you have success with it.
This one I recommend for high school students as it
contains VERY advanced graphs for things like
measuring rainfall and other phenomenon. It is the least
intimidating of all of them. Enter at your own risk. 
This site is just beautiful you can't print the graphs
you make but...
Ahhh! Finally a metric system site this has cm squares!