If your intent on having a pole then check out;

https://www.spotlightstores.com/nz/curtains-blinds/tracks/hand-drawn-tracks/tribeca-avenue-pole-track/BP80327984

Else, your best bet is to find a place that does free measure and quotes... 

I found Russels to be quite reasonable. Theres also Millers, Harveys etc etc... just google "curtains buy now NZ". 

Mate used to work at Martec ChCh, they do all sorts of rails for all the retailers

larknz: That looks like a standard curtain track screwed to a wooden rail. An extendable track may work, but a better quality track cut to the correct length may be better. Where are you? Different areas will have different suppliers.

Auckland. Where would I get the half wooden rail though?

Pretty much any wooden architrave or Trim/mouldings store will have them,

heck even Bunnings appear to stock them

https://www.bunnings.co.nz/pinetrim-18-x-6mm-2-4m-untreated-clear-pine-half-round_p00293524

Hm, thanks for the tip - I'm not sure if the dimensions would be the same, will need to check but what about the ends? Any ideas?