These are the screws I'm looking for: https://www.operationparts.com...ent-handguard-screw/

I have one of my ARs bought years ago with the URX II handguard but never paid attention that it lacked the two screws at the rear until recently, when I felt the bottom rail kind of rattle a little. Knight was really no help. Told me to check with Operation Parts, which is out of stock. Already signed up for email notification, but I have a feeling I will die of old age before they'll have it again. So, if you happen to have a couple, or if you know anyone having them in stock, I'd be grateful. Thanks.

It might be worth reaching out to Neil at 2AF.com.
904-593-6921

He always seems to have KAC parts and guns. If not he may be able to point you in the right direction.

Hope it helps!