To be honest you cant beat local knowledge for the bassing, and you could do worse then getting hold of Mike Bryant (flappy) in St.Columb but if you fish the estuary at Padstow at low tide and fish it back in you should pick up a few fish.
Mawgan Porth is also good, fish the river side there again low tide back in. (be careful and watchful as the tide can run around behind you)
Mullet can be got easy from Truro, go along the wharf past Tesco to the end and you will see them there.
But to be honest we Cornish are a bit secretive about the best marks as it took generations to find them, so a trip with mike might well pay off.
also try here
UKSWFF - Saltwater Flyfishing In The United Kingdom