Nashbar sells a thread steerer carbon bladed fork for about $100 with steerer lengths up to 240 mm. Look here: http://www.nashbar.com/bikes/Product...9_10000_202441

Otherwise, threadless forks in both steel and carbon are far more prevelent as are threadless stems these days. For the conversion you will need a new fork, stem, headset and probably some spacers. It's a fairly easy change.