Well if you stripped the screw out, putting a new one in is not going to help, it will probably fall right out as well.
Call your Energica dealer, they should be able to order you ANY part you need for the bike in theory.
Take another screw to the hardware store, Ace Hardware, Home Depot (good luck getting one of their retards to even know what a screw is let alone how to size it but anyways), and see if they got something in stock or can order it for you.
If you have looseness problems, you probably have bigger issues than just the screw, some locktite might be helpful as well. Don't get the hardening type that turns into concrete, but the stuff that will hold but you can break it loose when needed. That should take care of the loose issue but still let you take the cover off when you need to service, and also keep the screw from falling out again
Aaron