Support for creating a DevEUI in the console has been added in a recent update of The Things Stack Community Edition (TTS CE).
A maximum of 50 DevEUIs can be created per application.
If you need more DevEUIs either use the link provided by @descartes above or check the following post in the DevEUI for non-hardware assigned values topic.
For commercial purposes (e.g. device manufacturers) it is advised to purchase your own range of official DevEUIs.
UI for generating a DevEUI in the console:
