Risers are available on Ebay very cheap,$40 with the cap included and some even cheaper depending what you are looking for. Like ED said you will be getting HD risers with 1/2" thread in them and the stock hole in the top tree is 10mm. So either adapters or drill tree.

I learned all I need to know about life by killing smart people and eating their brains.
Eat right ,Exercise ,Stay fit, Die Anyway!