In order:
Sydney 4 teams
Brisbane 3 teams
Hunter
Gold Coast
Illawarra
Canberra
Gosford-Wyong
Sunshine Coast
Thats 13 and if I needed more then it would have to come from the following:
1 more from Sydney
Perth
Auckland
Melbourne
Far north Qld
This is based on the following population counts
Sydney 4,119,190
*Melbourne 3,592,591
Brisbane 1,763,131
*Perth 1,445,078
*Auckland 1,294,000
Newcastle-Hunter 589,239
Gold Coast 482,324
Illawarra 394,211
Canberra-Queanbeyan 368,129
Gosford-Wyong 297,956
Sunshine Coast 276,267
Far North Qld 231,152
The asterisk (*) is for populations where the supporter base is 'impaired' by other sports such as AFL and Union. I have also assumed a certain amount of impairment to the Sydney supporter base from piss-poor access to sporting grounds. I'm not going to name the teams that should and shouldn't make it.