have you tried Rockstar Tactical? I've found replacement sights for my 8.1 there... not sure about the T8, but it could be worth a try.
I have gone through their whole catalogue a few times. They have sights for the 8.1 but not the 8. I assume 8 sights are so hard to find because they are out of production. My best bet will probably be just to buy aftermarket.
Please sell me your smiley tipx plug! Please send me a PM!