I think their discontinued but dealers still have them as NOS. They are pricey. At least $30 each new. Check ebay for used transom screws. Check here for new screws: https://shop.evinrude.com/
You can buy allen head studs at hardware stores the same size and then buy a stout cupped washer with a hole just small enough so the bolt doesn't push through. My motor is set up like this because my clamps were getting in the way of my jackplate when I would slide it down. The allen head screws makes it harder to steal the motor since very few thieves are carrying around a big allen wrench.