RF, most special forces op's buy their own 'carry' as the issue stuff is invariably a bit naff... If a Busse was left behind anywhere the chundies (Tali/Insurgents etc) would go looking for Yanks because Brit' squadies can't afford them! A lot of the Tali etc are quite astute enough to surf to find out what stuff is...
I think individual units often order batches of knives, since they are not issued them. Just look at all the different Military overrun models.