Hi guy, this is stupid question, how can I clone the plan 9 source code? I checked official wiki it doesn't have any documentations for cloning using git etc. I am specifically interested into /sources/contrib/miller repository.

Let there be some light .../\...

There is a git repository with (a slight variant of) the Plan 9 distribution including all source code at https://github.com/0intro/plan9-contrib

Raspberry pi specific part of the kernel source is found in sys/src/9/bcm

This is not quite as up to date as the source in https://9p.io/sources/contrib/miller/9/bcm/ (also packaged for convenience into a single file as https://9p.io/sources/contrib/miller/9pi.tgz), but it should be ok unless you're looking for pi4 support.