Adafruit FLORA device extension, Arduino Micro .mext file needed


We want to use mBlock to program Adafruit FLORA V3 boards (AVR 32u4 cpu, 8MHz oscillator). This board is ‘almost the same’ as an Arduino Micro but it has a different crystal oscillator (Arduino Micro has a 16MHz one).
With a modified bootloader (original Arduino Micro, properly changing the frequency) mBlock uploads the code and everything works except those related with ‘timing issues’ (seconds get into ‘two seconds’ and serial communications get lost). mBlock code is sent assuming a 16MHz oscillator and no further operation is allowed (until we re-burn the bootloader with an external programmer).
How can we get the Device extension file (.mext) for Arduino Micro? The Arduino UNO we have (downloadable as example at extension builder) differs too much (different CPU) and needs a big effort to adapt to FLORA boards.
Thank You