Where can I find backlight Filter ''chip''?

All of a sudden, my tech are having problems with iPads that has half of the screen darkened after a glass remplacement ? It never happened before and since a month ago, we had 4 in only few weeks.

I am looking to replace the backlight filter chip on an iPad 4 and my regular supplier does not have it in stock, I am wondering where I can find this part and how much I am supposed to pay for such a tiny lifesaver ?

Thanks for you answers in advance for your help.