Cheaper and better just to replace the whole cooler. Anything that fits AM3/AM2+ mobo's and is short enough will work.
CPU Cooler: ARCTIC - Alpine 64 PLUS Fluid Dynamic Bearing CPU Cooler ($11.88 @ OutletPC)
Amd stock coolers were miserable, not doing a very good job at all unless running at full speeds (with its associated noise), so generally a 1/2way decent aftermarket cooler is usually recommended.