what is a mod suit?
http://www.google.ca/search?q=mod+suit
most mod suits are made at the tailor so you can get the fit and style you want perfectly. but if you wanted one off the peg, i would suggest the ones linked. especially the merc ones.
sorry..link.
http://www.ekmpowershop6.com/ekmps/shops/modclothin/suits-32-c.asp