Do you mean the long screws that hold the alternator to the motor block or the smaller short screws that hold the round cover that says "Yamaha" on it to the main left side cover? Both are just standard metric fasteners and may be available right at your local hardware store. As far as screw or bolt sizes go, Yamaha has included the size in many of the factory part numbers. Screw, bolt, washer, and nut part numbers usually consist of 3 sets of digits. The middle set contains the size. As an example, the alternator to motor block screw is part #98501-06075-00. The center set of digits, "06075", indicates this is an M6 screw that is 75mm long.