Overflow plates for a 240 Gallon?

I am getting ready to buy my 240 gallon tank but it is not drilled. So I need to find out where I can buy the overflow grates. I can't seem to find them anywhere. Anyone know where to get them?

 

I think I will try these. Has anybody else tried them?

http://www.glass-holes.com/category.sc?categoryId=3

 

Thanks Bill,
Has anyone tried the
Figure 7b: Horizontal Overflow (with overflows fitted in)
pictured at Bills link? This is what I am planning on getting at Glass-Holes.com, seems like the same concept anyway. The venting is on the outside of the aquarium in the elbow. They claim they are very queit and it seems to be the same concept as the Durso.