Here's her response.
"Hey again! Just heard back from the publicist -- the sweatshirt is J. Crew but is actually from the men's section; originally intended to be a wardrobe item for Tom Hardy, but Reese ended up wearing instead. Hope that helps!"
Which leaves us with investigating the J. Crew website.
I haven't been able to find THIS EXACT SWEATSHIRT, but...
Here are some links to stuff that's similar:
Fleece & Hoodies
Sweaters & Hoodies
This does look close! though lacks a hood
As does this one, except it has a pocket and Reese's didn't
Well. This is as far as I'm going to hunt for this. If you happen to do a more extensive search and come up with what you think is the exact sweatshirt, hit me up: firstname.lastname@example.org. Or you can post in the comments section. All credit will go to you.
And, if you have a Twitter, take a few seconds and thank Kate Hogan for you help!
For the full inquiry about the fashion of This Means War, click here