What size are the Huawei Watch 2 case screws

You might try a method I found to work sometimes, writing a nice (honest) letter to their customer support telling them how much you enjoy their product but sadly you are missing said screws. With a bit of luck you will get a thank you in reply along with a new set of screws in the mail. Depends on the manufacturer of course, but some companies value the positive customer relations over any “effort” that might take.