nice tank :bounce:
the filter you want is available in NZ if you ask one of the major retailers to order it in for you. but the FX5 is also fantastic. it offers everything you would expect - and comes on special from time to time, so can even be purchased reasonably. the warranty is pretty solid, and you never have to worry about Fluval pulling a filter off the market, leaving you hanging with no spare parts... their part retention guarantee is for 10 years, which is really decent.
how many litres is your tank? you could look at getting 2 FX5's if you had to resort to that.
I have 2x405's on a 200L 4ft. tank, and there are no problems with my fish being flung across the tank cause of the water flow, so you need not worry about that happening with oscars.