Create a rule to filter by page source information

Lately, I’ve been receiving a lot of spam with chinese and korean character sets. I’ve read that an effective way to filter them out is to search for things like charset=ks_c_5601-1987 and charset=“gb2312” in the page source (internet header).

Does anyone know how to create a rule that can search the page source of incoming email?

Thanks,

Shawn