You've probably seen people use this before. Now, you think it'd be an uncommon or rare occurrence, but in reality, it's too damn common. So much so that they no longer realize that they're dismantling proper sentence structure very slowly, and people who correctly word their phrases with "should have" are becoming less common, or maybe even extinct on the internet as we know it.
So you people should have realized that "should of" is not a replacement for "should have/should've".
TL;DR: "Should of" is not the correct wording, "should have" is.
gorp