Well, I know Harvey tends to wear Tom Ford suits. As for Mike's wardrobe, I'm not sure they've ever mentioned publicly their preferred label for him.
On a guess, I'd say possibly D&G.
Here's what I do know about most of Mike's suits from observation:
-Slim/European cut
-2-Button
-No vest
-Slim notch lapels
-Single vent (Thought this isn't hard and fast off the top of my head)
-Flapped pockets
-Flat-front pants without a bottom cuff
Tie:
-Slim (but not skinny) tie...approximately 2.5" wide at the base
-Season One he almost exclusively wore a four-in-hand knot, Season 2 he switches it up between a four in hand and Windsor knot depending on the tie or where he's wearing it to. I haven't noticed anything that appears to be a Half-Windsor knot on the show, but I could be wrong.
Shirts:
-European/Fitted cut (Or just tailored)
-No front pocket
-Medium Straight (Sometimes called a standard spread) or button-down collar (A traditional straight collar would be a bit too narrow in my opinion) with an occasional medium spread collar thrown in. (I think over the seasons, they are slowly working him towards a spread collar as an symbol of him taking on the suit as Harvey has)
That's about it. I'll see if I can dig up anything, or I'll just keep my eyes open during the next episode.
-Nick