Do you know what kind of screws they are?
Most standard screws can be purchased quite cheaply from Laptopscrews.com, like m2's, m2.5's, etc, of various lengths and head shapes.
Bizarre screws, like some of those used on laptop heatsinks, that have some weird combination of a head, a guard stop and the thread, can't usually be bought there.
They have perfect screws for reference AMD Vega64 and 5700 XT video cards (X-bracket, PCB, etc).
I had the same overheating issues with this card as time went on. I tried contacting ASUS to get replacement screws and they told me to send the card in to them for warranty repair. Just mailed it off yesterday.