For the left arm I started with the other regular sergeant arm and cut/filed away the sergeant stripes and cut away the chainsword. I then took the laspistol (which I had left over from the right arm conversion) and after cutting away the right hand, glued it in place. I then had to do a bit of tricky filling/sculpting with some greenstuff to make the trigger finger look right, and also reshape the handle.
The banner itself is straight from a bretonian (WHFB) command sprue - though I had to cut/file away the hand attatched to it. I also added a purity seal from the marine (tactical upgrade) sprue I have lying around – just to make it look a little more like the one pictured in the codex.