The clamp screws are m3 x 10, 24 required. The ones securing the plate are the hard ones because they are a "shoulder" screw of a special Tarot type where the shoulder has a larger diameter than the threads to recess into the carbon plate for alignment. The actual dimensions are listed as m2.5 x 5, 24 required, and called out as "round six angle screws stage" in the instructions. Looks like two different screw sizes were used on your motor mount plate. The one that sits low on the plate is the correct one.
If you have the horizontally folding 810 they are the same screws as those used on the top plate to secure the top of the 4 arm pivot lock clamp mechanisms, which are also called out as a folding arm lock assembly elsewhere in the instructions. In that location they are called out as "shoulder hex cap screws". They don't like to name anything the same twice... Attached is a page from the instructions. If you can't find the screws consider buying some m2,5 x 6 and using a flat washer with each screw. Don't go crazy with lots of Loctite, use it sparingly.
BTW, if you rotate the motor 180* the motor wires will run straight into the boom at the top of the plate on the motor mount. Doing that eliminates the chance of the outside edge of the mount cutting a wire in a roll over. You will roll it over at some point.