It was some time ago that I sourced mine from an overseas supplier (Japan) but unfortunately I don’t have the details.
Have you tried asking your local florist because they often brand their ribbons? I think that’s where I got my referral from. Hope that helps if you don’t get any solid referrals.
There’s no shortage of ribbon wholesale suppliers online for the arts and craft businesses. They normally deal with other businesses but it’s worth trying as long as you have the schools ABN number.