Speaking of defunct distilleries, I managed to pick up a bottle of Port Ellen on a trip to Scotland last year, I found it in the giftshop at the Edradour distillery. The PE was a gift for my dad so I get to sample it on visits home
And, because a distellery is closed does't mean there is no supply of their product. independent bottlers, like Cadenhead, own casks which they bottle for sale. In addition, closed distilleries may contain large amounts of whisky as was the case with Ardbeg when purchased by another active distillery or company.
Also, just spent the weekend with friends who opened their Laphroig 15 -- ICK!! Not for me. We had it in a comparison tasting with the Highland Park and it was totally overwhelming.