A few years back was able to get the afternoon school bus which left Thredbo Info Centre to Jindabyne on weekdays at 4.30.
At the time this was operated by Snowlinkshuttle. Try
info@snowlinkshuttle.com.auThe cost was $20 and no booking needed (its an otherwise empty bus returning to Jindy). Obviously doesn't run during school holidays. You may also be able to use it to get from Jindy to Thredbo in the morning.