Unfortunately there is no public transport between the two areas, and hitch-hiking in a pandemic is unlikely to be productive. Get adventurous and take camping kit; or just sleeping bags and doss under big rock shelters at the top of Loch Avon - go via Glen Lui and Glen Derry to Loch Etchachan and over to Loch Avon, then over the hill to Glen More or the Cairngorm Ski area, thus over by the Chalamain Gap to the start of the Lairig Ghru, back eastward through the Lairig Grhu and over the shoulder of Cairn a Mhaim to Derry Lodge and back down the track to the car park at Linn O' Dee. All very impressive scenery and interesting terrain. Do not go via the Chest O'Dee and River Dee from Corrour to Linn O'Dee, as this is a vast, flat, dreary trudge of no interest which will sap your will to live until you collapse, footsore and weary, by the wayside, begging a passing deer stalker to put an end to your misery with a bullet in the brain.