If your school can make use of mentors or coaches to support pupils, consider the local church as a possible source of suitable people. Given the diversity of people in a church, a congregation will often have a number of people who could support pupils as mentors. There may be active retired people who are keen to be of use, and who want stimulating environments, such as a school, where they can volunteer. They will probably have valuable wisdom and life experience to offer. Many church members will also have suitable expertise to support as coaches. The church may also provide you with a pool of reliable men willing to offer as a mentor if you are in the predominantly all-female environment of many primary schools, or have a significant proportion of boys who have no father in their home environment.
Some employers will allow employees time out of work to be a mentor at a local school, particularly if the company also has a link with the school.
Since mentoring may be a new experience for volunteers, your school should offer training and advice for people who volunteer.