As you like Islays and hire a car I would suggest that you spend a couple of days there and go by ferry from Kennacraig then you could visit the Loch Fyne whisky shop
http://www.lfw.co.uk/
or if you're in Speyside visit Gordon and MacPhails shop in Elgin
http://www.gordonandmacphail.com/
Both have excellent stocks of rare whiskies