They're not Explorer / Day Rover tickets. They're Transport North East tickets. They'll not be finding them as they'll be looking under the Network One menu which has about 50 tickets in it. I haven't asked for them but the ticket types are:

Transport North East All Zones (£6.80)
Transport North East T&W (£6.00)
Transport North East Northumberland (£5.00)
Transport North East Durham County (£4.00)