Supercheap can mix up paint for you, but it will depend on whether they have the "recipe" in their paint system for the colour you want. They will identify it by a colour code for a make/model of a car. There is a website where you can find the colour codes for automotive colours, and you can find Pelham blue there (from the a 1960 Caddilac) - https://paintref.com/cgi-bin/colorco...m+blue&rows=50. You could try giving them one of those codes and see if they can mix it.
Since you are in Sydney, VG Auto paints also do Acrylic paint mixes, and may be able to help you out as well. Since they have a different brand, they may have the recipe if supercheap don't have it. https://vgautopaints.com.au/