Inverness Airport - The closest airport to Gairloch is Inverness airport which is about 90 minutes drive. Its a lovely drive travelling from the East coast to the West.
Edinburgh Airport - This is around 4 and a half hours drive straight up the A9.
Glasgow Airport - This airport is just over 5 hours drive up the A9 or alternatively you can drive through Loch Lomond National Park for a slightly journey time of 5 and a half hours.
Aberdeen Airport - Just under 4 hours away is Aberdeen airport. This route takes you along the Moray Firth coastline. If you are looking for somewhere to stop, Findhorn is a lovely coastal vilage. A slightly longer journey will take you over the mountain passes.
You can drive all the way to Gairloch. From South of the border it is normally best to drive up through the Lake District and across from Glasgow towards the A9. Once you're on the A9 its up to Inverness then along to Garve, Achnasheen, Kinlochewe and finally Gairloch. There is a lovely view point after Achnasheen before the road descends into Kinlochew with fantastic views along Loch Maree.