Hope this adds to the good advise already from @Joey_van_der_Gaag
Here is the same antennas on the manufactures mount.
In Australia you need to be installing 45Deg off the horizontal with the two antennas 90Deg opposed for best results as shown in this photo, in Australia if you mount so the fins are flat on the Horizontal, then you will get almost no performance out of the antenna (and in most parts of the world this would be the same too).
You can source this from many antenna suppliers around the world, be wary of cheaper imitations (such as pot riveted and spot welded version), they will have a specification sheet saying they preform better, though we know from real life experiences that the RFI antennas are the the Genuine thing.
Here are some the links to the Australian manufactures website if interested.
And a trusted supplier that sells them in Australia and also internationally as a Kit is linked here
Happy to Help,
Marcus 