Could someone please direct me to a written code requirement outlining the bonding of metal studs when non-metallic electrical boxes and wiring are installed within the walls?

I don't think that 250.104 [C] or D, [2] applies here, since these metal studs are partitions, they are not really structural and are also normally faced with drywall so are not exposed.

I remember this subject being brought up at a code seminar several years ago, and it was recommended that if NM boxes were used, a tail should be extended from a branch circuit equipment grounding conductor in one of the boxes and attached to one metal stud in the wall with a lug or machine screw, but I can't recall if there was an actual reference to this in the NEC though. Obviously this is less of an issue when metal boxes are used.

Thanks