Usually setback posts are 25mm. To get more is hard. FSA makes or made a couple with 32mm or more. Rivendell sells a pricey Nitto 40mm that wouldn't look right on that bike. Look Ergopost has adjustable setback to 40 mm, see eBay. There are some less common seatposts with even more.

If you flatten the saddle, you may find yourself sitting a bit further back on it.

Edit: FSA K-Force carbon post has a 32 mm version. Pretty darn expensive, like >$130 new. Might find on used on eBay. Look Ergoposts are going for >$100 on eBay. Those are the only ones I can think of that would look right on that bike.