lol, dude really?
not to mention it's what she wants as well since, again, that is what is the "norm" in the NE USA.
i have never seen mismatched groomsman in real life and to be quite honest i think it looks fairly terrible in the photos i've seen. that's not to say it isn't the right approach, more convenient (for some) and can't be done well.
Your comments are at odds with themselves.
At once you say it looks terrible from what you've seen and then indicate that's not to say it can't be done well.
No one is saying they need to be mismatched, just coordinated. It's your wedding. You've been hanging out here long enough to have some idea of what coordination means. Do your homework. Have you spoke to your groomsmen? Do they have a charcoal or otherwise dark suit in their closets.
Otherwise, oblige your groomsmen to go out and spend money for your big day, or better yet pony up your own cash and explain to the newly minted Mrs. why you need to hold off on buying new things for your home because she and her mom thought that the groomsmen needed to match one another.
Someone else mentioned renting. A good option.