Thanks for your help.
I added Raspberry Pi foundation into /etc/apt/sources.list:
deb http://apt.osmc.tv/ jessie main
deb http://mirrordirector.raspbian.org/raspbian/ jessie main contrib non-free rpi
deb http://archive.raspberrypi.org/debian jessie main
I still have an error but I am able to update and find the package
W: GPG error: http://archive.raspberrypi.org jessie InRelease: The following signatures couldn't be verified because the public key is not available: NO_PUBKEY 82B129927FA3303E
One last VERY IMPORTANT remark, if you try to install “sense-hat” it will overwrite OSMC firmware with classic firmware.
You can safely install “python-sense-hat” and/or “python3-sense-hat”, it will install all C and Python libs without changing your firmware.
I did not verified if the sense-hat is fully functionall on OSMC yet 