If you have an old Tamagotchi you can take it apart (VERY CAREFULLY!) and use the buttons from it. It looks like the buttons have not changed at all since V1. You would need to use jewelry screwdrivers and be very, very careful to put everything back exactly the way it was. The buttons are one piece, a rubber thingy with three big bumps sticking out.
With my first Tam I took it apart to paint it. But it is scary, you have to put it back exactly right or you will break it so be super careful.