If a political party, or combination of political parties, truly wanted a referendum they could just run one. It wouldn’t be governed by any legislation, but who cares? It would be just as powerful as a CIR (which relies on expressing public opinion and is not binding).
Political parties have access to electoral rolls, parliamentary service funding for material and postage, and free mail for people returning material to parliamentary addresses.
The parties would probably want  to find some eminent people for a panel to oversee the decision on the question and the rules under which the referendum will be run. They’d also benefit from maximum transparency: invite in all the media who want to be there, ensure all meetings are open, all agendas and minutes are public, and so on.
Figuring out the question’s gonna be tough; that’s the key to a referendum and worth putting time and effort into consultation and getting it right.
But, seriously, just do it!
It doesn’t matter that National and Act don’t want one, run it anyway!
It doesn’t matter that National and Act will say it’s not binding, would they ignore the outcome?
Just do it!