where can i go to get a petition to let my boyfriend sign over his rights to his son?
First the legal advice: There is no such thing.
When your boyfriend had a child, he has a legal obligation that cannot be terminated to support that child until age 18 (in some cases 20). Unless the cild is given up for adoption, nothing terminates that child's right to get support from him.
Some non-legal advice: a boyfriend who thinks he can get by with not supporting his child is not someone any woman would want to be involved with.