No such animal as a threadless to threaded adapter, however, you can buy a threadless steerer tube extender to raise the stem height. The problem with a quill stem is that it is designed to fit inside the steerer tube, and a threadless headset requires the adjuster to also fit inside the steerer tube with the stem clamping on the outside.

http://www.bikeparts.com/search_resu...p?id=BPC304168

http://www.bikeparts.com/search_resu...p?id=BPC304170