I am not sure what class you are checking, whether it be reward (U), D or full J seats.

According to the QF timetable QF58 from WLG to BNE only operates on Thursday, Saturday and Tuesday. It may be possible that this service is only sold as a single class, or that J is sold out for each day that you have tried.

The other options would be via SYD or MEL from WLG or via AKL. Each offer a daily connecting service. Personally I would take WLG-AKL-BNE as AKL-BNE is operated by a 744 with full international (but not skybed) config. This would require an overnight in AKL and a Y ticket from WLG to AKL (50 min flight) as J is not offered domestically in NZ.

Personally I would not pay for J on a Jetconnect operated service. It is not worth either the FF points or $$$ as it is similiar to F on an AA 757 or BA Club Europe.