Looking at the parts fiche at MAX BMW ...
BMW Parts for your C650GT 16 (K19) Production: 12/14-07/20 USA
shop.maxbmw.com
... it doesn't appear to me to show that bracket and its screws:
View attachment 6132
My
guess is:
1) That bracket is considered part of the radiator, i.e., it would come already attached, if someone were to buy a new radiator.
2) That there's nothing particularly special about those two screws, except that they are short. My guess is that they're a standard thread pitch, perhaps M4 or maybe smaller, self-tapping metal screws.
That's my guess, anyway.
Did you personally separate that bracket from being attached underneath the radiator, or did it fall off, or is there some other story behind all of this?
I own a C 400 GT, not your C 650 GT, so I can't just take a look. Hopefully someone who owns a 650 and has the bodywork off can take out one of those screws, measure its length and width, and take a photo for you.