The best option is to buy the physical book. Many online Indian bookstores (like , Shruti Sruthi , or Nattuvangam ) ship internationally. The cost is typically very reasonable ($10–$20 USD per volume).
If you are looking for an English PDF version or a guide to using this book, ganamrutha bodhini english pdf
As for the English PDF version of Ganamrutha Bodhini, I couldn't find any direct links to download the PDF. However, I can suggest some possible sources where you might find the content: The best option is to buy the physical book