There is no such phrase as should of.
It's fucking should have. Modal auxiliaries never have an ' of ' after them ( except for special cases such as ' He ate as much as he could of his mom's cake' ). They're always followed by a verb. And as far as I know, ' of ' isn't a verb ( I of, you of, he / she / it ofs, we of, they of? No. ). So please, if you tend to say or write sentences like this, always proofread your posts & make sure you do not oppress the english language any longer.
Thank you.