VFR training aircraft inbound to ROA; awaiting ATC clearance into the Class C; experienced an NMAC with the same type VFR aircraft also awaiting Class C entry.

Narrative

Returning to ROA from IFR training at MTV with IFR student 'under the hood'; radioed ROA Approach Control 25 NM south. ROA instructed; 'remain VFR & remain clear of ROA class C'. We turned east to align with the final for the ILS 33 awaiting permission to enter Class C. Called ROA again in 15 minutes and requested; 'For planning purposes; when can we expect clearance into Class C' and received no answer or squawk code. Subsequently; Aircraft Y also southeast of ROA on an air photo mission called ROA approach; and was also advised to remain VFR and clear of Class C. We made several 90 degree turns outside of Class C but in the vicinity of the ILS final approach course. On a heading of east at 3500 MSL; I detected an aircraft at my 9 o'clock position; just above my wing; about 50' horizontal and immediately initiated a hard dive. Aircraft Y passed just above my wing. Subsequently; both of us were given squawk codes; allowed into Class C and landed without incident. SEE & AVOID cannot be taught enough! I believe that a contributing factor was that the controller was a trainee with a moderate workload and held us in an area of some traffic without mode C identification despite both aircraft having requested same.