If memory serves correct, very few. Most of TM's fumbles happened when he left the pocket, whether by designed run or scrambling. I can think of a couple scrap examples where he was blindsided in a throw and lost the ball, but that was irregular. He typically has poor ball handling skills when running.
I'm about 90% positive exactly 2 were from blind sides in the pocket. Just from casual observation it seems like half his fumbles come when he gets near the sideline. I don't know what it is but he always seems fumbles going out of bounds or fumbles the ball out of bounds. Of course those aren't turnovers so it's not as big of a deal, but it's still a ball security issue.
I watched the Southern Miss game and the Arkansas State game on DVR in the last two weeks and off the top of my head I can remember two blindside hit/fumbles in the Ark State game alone. One accounted for Ark State's first TD and the other killed a Husker drive in the red zone.
I find it awfully hard to believe that it only happened twice and both happened in the same game.
Maybe I'm thinking of blind side turnovers, that's probably it actually.