Exactly the same thing happened to me today with the G915. One pin of the left shift key broke off. Luckily it happened just 4 months before the warranty expired...
Logitech does not supply individual parts, as I was told on the Logitech phone. It's a bit embarrassing when you have to replace the whole keyboard because a small piece of plastic broke off. Well, I hope the keyboard lasts another 2 years.

I think you'd have to ask Logitech directly.