Ok, if you don`t want to buy a fork (but I think that would be good upfront if you are mainly doing road and light trails) you will have to buy a fork crown stem converter from for example PROFILE.
Then buy a 31.8 stem and handle bar. 31.8 is the oversize but looks great.
eg. only....
http://www.chainreactioncycles.com/M...?ModelID=62289
http://www.chainreactioncycles.com/M...?ModelID=19856
if you don't get a new fork, then something like this. I'm sorry but you will have to ask a shop maybe about your current fork quil / crown size for this qizmo...
http://www.ebay.com/itm/Profile-Desi...item4ab7e232c4
Oh also to be on the safe side, buy a couple of 5mm spacers in case you have to take up some gap under the stem and headset. (like the red one I have in the first pic.