Yes I wish I could help you with source. Here in the US it’s as easy as ordering from Amazon.Wow. This is such a valuable resource. Thanks for sharing. I just need to find a good source for Sodium Hydroxide in my country and when I do I will brew my perfect batch.
I may even go with 6.0 pH since this paper shows that at 5 degrees C and 6.4 pH it stays stable for at least 3 months.
US6835811B1 - Extended storage of reduced glutathione solutions - Google Patents