How to get this/these block(s)?

You cannot get those blocks in the Overworld without mods. The Ender Crystal is an entity and, for that reason, cannot be collected. It also cannot be crafted.

There are some mods that let you place entities as you wish, at least on the server-side.

This is called an Ender Crystal. It is not a block but an entity and can be spawned in using

/summon EnderCrystal

You can use single player commands. It's a command mod that is very useful for the ability to spawn entities and other uses.

There is an automatic installer that back-ups your minecraft.jar and worlds in case you change you mind.