Finally I find a working workaround!
Start Ubuntu Mate from “old” Pi 3 Model B and run the command
sudo BRANCH=stable rpi-update
This will install the needed files in /boot/ with the same kernel version of raspbian stretch.
The integrated wifi will not work because the correct firmware is not present in Ubuntu Mate i think;
I solved with a simple copy&paste from a fresh Raspbian Stretch SD.
Not knowing exactly wich are the missing files I simple did a join of the two folders /lib/firmware/brcm