@Valentin-Haenel As indicated by @Zheng-Han , it is possible to create your own copy of the firmware using the instructions he gives - I have successfully done so and installed and tested it on my Omega.
Be warned that this is not a trivial procedure and you will need to ensure that your package selection is correct otherwise you may have problems running the Omega.
Also, firmware built doing this will lack any of the Omega branding and customisations - partly because the core code is not Omega specific (a copy of the official repository has been requested but is not forthcoming yet) and partly because it is unclear as to precisely what packages need to be included.
If you do manage to get a copy of the firmware built and installed and running on your Omega, you may well need to get you Omega back to running an official copy of the firmware at some stage. You can do this as follows:Copy the most recent Omega firmware image from http://repo.onion.io/omega/images/ - probably omega-v0.0.6-b277.bin and copy it to your Omega to the /tmp directory On your Omega, from the /tmp directory, run sysupgrade <image-file-name> where <image-file-name> is the name of the image file copied as above and wait for your Omega to reboot - will take some while.