The last time I was up that way, there was a Gleaner in Kyle of Lochalsh and in Portree. Think gleaner is connected to Shell as they rebranded a lot of rural Shell petrol stations to Gleaner.
On the supermarket fuel argument, I worked on forecourts for a few years and speaking to the pump engineers they never filled up at a supermarket, they said, the pumps are always gummed up from pumping the petrol, what does that do to the car. They used the big brands because the pumps where always cleaner. Guess this is all the additives they add above the standard fuel standard. only my tuppence worth