This is an awesome dream! I hope someone can help you out with it...I seriously looked high and low for renting. The only options I really found were buying them from ebay or stalking used clothing stores....but hard if needing them for groomsmen.
I know I found a few options at http://theleesshop.com/index.php and http://us.asos.com/ at one point.
The only people that I know were able to do this on WW were people that bought suits at specialty stores.