Question: I know that in a previous version of Minecraft, you could get a Ender Dragon spawn egg (a white egg, like it has no texture). Is that still possible, and if how do i get it?

Answer: 
### There's no Ender Dragon Spawn Egg since 1.2

Reading the page on [Spawn Eggs](http://minecraft.gamepedia.com/Spawn_Egg#Ability_to_spawn) on the Wiki, it does not seem possible to get an Ender Dragon Spawn Egg since version 1.2.

Specifically,

> 
> **Any entity not in the list above**, such as paintings, entity blocks, or primed TNT, **cannot be created with spawn eggs**, even if set to the relevant entity ID value by commands. The egg is colored gray (Spawn Null.png) and will only work in version 1.1.
> 
> 
> 

(emphasis mine)

As far as I can tell, the list is identical with the spawn eggs you can get in creative mode. Ender Dragon is not listed, and can not be spawned using spawn eggs.
As of 1.19.3, you can now obtain them with the `/give` command.