Yeah, it's a present to an American
So, Brewdog Scotch Ale...can that be found most supermarkets?
If it's a present, then I really wouldn't bother with anything but that to be honest. Be a bit of a waste of time/money/effort sending anything else over. It's all a bit 'meh' to be honest. Plus, Scotch Ale is quite a broad description. Most people won't know what it is like they understand Porter (Stout), IPA or bitter for example.
Now, how are you actually going to get some. No, you won't find it in any supermarket. There'll be a shop in your city which sells some I'm sure. I'll be going into my booze shop tomorrow who should have it so I can check their price/availability. They'll sell over the phone (they don't do online sales) and send it to you. You could order from the Brewdog site direct but last time I checked their postage was lolworthy.
Let me check Tesco/ASDA online and see what they have for sale in terms of 'Scotch' ale. To clarify, you want something in the Scotch Ale style rather than a Scottish beer?
Edit - There doesn't seem to be any 'Scotch Ales' on Tesco/ASDA online though I'm sure I've seen Belhaven being sold in store before. If you are just after Scottish beers then buy whatever Brewdog and/or Innes and Gunn they have.