Fraternity/Sorority Composite Clothing Help

I have done a few sorority composites for some local groups at my old school, but they were all very small and I could make due with makeshift draping. However, I've been asked to shoot composite photos for much larger groups and would like to come across as more professional. Plus, I now have a Fraternity interested. Can anyone help me locate where I can purchase drapes and one-size-fits-all suits/jackets for men?

You're not going to find any one-size-fits-all suits or jackets. None that look good anyway. There's just no such thing.

You might be able to get away with having three or four different sizes on hand (small, medium, large, XL), but even then they're not going to look properly fitted across all the different fraternity members.