Most of the GSH is stored/synthasized in cytosol. GSH is present in cytosol, endosomes/lysosomes, and mitochondria. The intracellular distribution of GSH in different organelles depends on the cell type.

The majority of GSH is usually found in the cytosol 1-10mM because cytosol is the principle site of GSH biosynthesis.Both endosomal and lysosomal environment  unlike cytosol are generally acidic and oxidizing which not favorable for reduction of oxidizedGSSG to Reduced GSH typically the ratio GSH/GSSG around 1:1 to3:1 in endosomal and lysosomes compare to the nearly neutral cytosol which usually the ratio 25-30

Thanks for all your answers. It helped me a lot!