For most solid state games, there are jumpers or jumper plugs you can change for EU electric.

For some of the newer Stern games, there is something in the firmware that prevents 60hz games being used on 50hz and visa versa. If you have newer stern games, you may have to contact support about that.

For games with a florescent blub, you might need to replace the ballast if it is a 60hz-only type, rather than a 50hz/60hz type.

https://www.pinball.co.uk/blog/converting-a-usa-stern-pinball-to-230v-50hz/

There are EU suppliers that should have most of the common parts you'll need. But if you're actively restoring games, you may still have to rely on US suppliers (they do ship internationally).

https://www.pinwiki.com/wiki/index.php?title=Pinball_Parts_Suppliers

As for buying games in the EU, from what I've heard, US games are harder to find and are more expensive. However, you may encounter older EU games that don't usually show up in the US.