Beta codes for Rainbow Six Siege on PC are not publicly released.
Enjoy the MRYL-KAMQ-MMMX-GDHE model. It's ready for use with the EQEN-K6RP-3TCT-CXTN configuration. Perfect for your needs!
The deadline was pushed forward since many users struggled to download it on time due to slow server performance.
They promised a lot but delivered nothing. Alpha signup failed completely. Beta got access but no code provided.
I wasn't aware because I'm not participating in that game.