I went searching for replacement glass because I thought there could be no way Kanger made a glass
tank without replacement glass.. but I didn't find anything. I'm really shocked they don't stock replacement glass for the Giants.
About a custom glass replacement.. I would assume any kind of custom glass, even at that size, would cost more than getting a new
tank altogether.
I wish I could help you out. If I were you I would contact Kangertech and explain your situation. Surprisingly, their customer service is pretty solid. I broke a couple metal parts on my mini protanks and they sent me replacement bases. If you ask for replacement glass, they might offer to send you it for free, given that you purchase something else.