Hi Rumen,
I was also wandering how to add lx_block to my runtime. I cannot seem to find the corresponding depot url to put in my archives file. The closest I found was _/src/lx_block in repos/os/recipes/pkg/test-lx_block/ archives, but from what I can tell that is relative to test-lx_block.
The depot recipe is in repos/os/recipes/src/lx_block. Since this, however, is not part of Sculpt OS nor the Goa release, it is not published on the genodelabs depot. You therefore have to build it yourself using tool/depot/create (see Section 5.5 of Genode Foundations).
Cheers Johannes