Gerstley Borate

My supply of G.B. is almost exhasted and was quite relieved when I read
recently that it was becoming available again, however my local supplier in
Hamilton, New Zealand, is not aware of any news like that. He also said
that he had not had good comments from customers about the use of
substitutes and he is not stocking any substitutes at the moment.
I use it in some C6 and raku glazes. Two questions...........
Is anyone able to confirm that G.B. is available again?
What is the most successful substitute that you have found?
Thanks in advance, Hugh.