greeting students on the first day of class would be a great time to ask for referrals.
Talking to your students throughout there experience and training to ask if there anyone else in there life would like to change there life situation and benefit from furthing there education.
Setting up referral tables in the lobby during students' lunch and break times are an excellent way to talk to students about referrals.
Visit their classes. Maybe have student appreciation weeks with food etc. Try to obtain referrals by interacting and asking students who have good experiences already at school about friends etc.
A really great idea is to just mingle with the students. Often conversation brings up referrals from current students.
During orientation when the student is very excited about starting your school and as they are filling out some paperwork, we give out a referal sheet and tell them to list anyone they know that may be a good fit for our school.