The RN number (the registered identification number) often found on a suit label tell you who made the suit. You can look up at:
http://www.ftc.gov/bcp/rn/index.shtml
In most cases, the company on the label made the suit - i.e. Tyr suit was made by Tyr (their RN is 77370), but I was surprised to see that a Nike suit was made by Jantzen (it's a polyester suit made about a decade ago)
I wonder if there are some companies that makes suits for many brands but does not put their own name on it? Especially for private brand labels or for stores like Kiefer.