What is the most effective kit or method for extracting RNA from a very small number of cells?
Well i depends how small number it is. Personally reccomed using some kind of TRI reagent(https://www.sigmaaldrich.com/PL/pl/product/sigma/93289). Never failed me. If you want to be extra sure you can use columns QIAGEN kits, they excell in nucleic acid isolation, and according to the internet they are available in Australia.
Bartosz Kazimierz Słowikowski answer is on the correct track. I will add to use a kit where it allows for the smallest elution volume ("minelute"). Qiagen offers RNA clean-up kits that offer minelute options. I have only used Qiagen's RNA cleanup kit with minelute option.
I frequently use Zymo's direct-zol kits for purifying RNA from bacteria cells. I found that the company offers a minelute kit, link below. I personally haven't used this kit but I am sure it would be useful for you. I have always used Zymo's kits to purify RNA for NGS experiments.
https://www.zymoresearch.com/collections/direct-zol-rna-kits/products/direct-zol-rna-microprep-kits
miRNeasy Tissue/Cells Advanced Kits
For phenol-free purification of micro RNA and total RNA from tissues and cells, including small samples.
RNeasy Plus Mini Kit
RNeasy Plus Kits are next-generation QIAGEN RNA extraction kits, that combine high-quality RNA purification with effective gDNA removal with unique gDNA Eliminator columns or plates. Total RNA of high purity and yield is obtained from a wide range of cultured cells and easy-to-lyse tissues. The RNeasy Plus Micro Kit is specially designed for limited amounts of samples and isolates up to 45 µg pure total RNA The RNeasy Plus Mini Kit purifies up to 100 µg total RNA (>200 nt) from a single extraction with efficient gDNA removal. Both kits can be automated on the QIAcube Connect and samples can be conveniently stabilized using RNAprotect Tissue Reagent or Allprotect Tissue Reagent and efficiently disrupted using a TissueRuptor II or TissueLyser II or LT system (available separately). The RNeasy Plus 96 Kit is for high-throughput purification of total RNA from cultured cells grown in 96-well plates.