I found this part on ebay.
Polaris Sportsman 600 4x4 04 Brush Guard 124399: eBay Motors (item 110562945967 end time Aug-20-10 12:19:23 PDT).
It says it is for a '04 Sportsman 600 and looks exactly like my '06 Sportsman 450. I checked the Polaris part numbers on both and the part numbers are different. Can anyone tell me what the difference in the two parts is or if it will in fact work on my 450? Any help or advice would be greatly appreciated.