My stock fan doesn't look like that, and i bought it the other day.
Mine looks like this:http://techreport.com/r.x/phenom-ii-x4-955/stock-hsf.jpg
you can easily pop the fan off and replace it, its the rig holding the fan that seems difficult to replace.
Edit: my bad, jumped the gun on what those were pictures of. If you wanna know the fan size, just measure it with a ruler.
Edit 2: I guess my original statement was right, the fans posted above are older. As for a new fan, i think you can get a new 3rd party cooler for next to nothing these days that will be sufficient for a mild overclock.