Check with agencies in your community to find out if they provide speakers on these topics. Your public library can be a great resource. If you have a Family Life Council or a similar agency that provides parenting education, it may already have a list of speakers to recommend. Many communities have drama and puppetry groups that present programs to children on these issues; check with college and university drama departments for help with contacting such groups.
Check also with your mental health department or your local Mental Health Association. If they don't have speakers to suggest, they may be able to recommend psychologists either affiliated with them or in private practice in your community. Many colleges and universities also have faculty members who are willing to speak to school groups; ask the receptionist at the main number if there is a speakers' bureau associated with the university. If there isn't, talk directly with someone in either the psychology or the education department.
Another resource is your city or county PTA council. Ask for contact information for speakers who have been successful in visits to other schools in your area. They may also have information sent to them by speakers who will come to your school for a fee.