LAST EDITED ON Jul-07-11 AT 10:21 AM (EDT)
 
>Have I missed anything ?

From chapter 1, when Kaname and Lindsey first relieve Sarge of the weapon:

"Where'd a punk like you steal an A&K Mark 23? This is a CID Lensman's gun."

(emphasis mine) While I could still be wrong, I would assume that while not all CID are Lensmen, only CID who ARE lensmen carry this particular weapon, just like only undercover Zardon Detective Judges carry the Lawgiver-C