But i'd like to try an Bottle of Guinness Special Extra, which is 8%abv
It's Special Export, and it's quite hard to find as it's not sold by Diageo. Occasionally specialist off licences will have some (eg the Abbot's in Cork) but it's sporadic. Your best bet is to get someone who is travelling in Belgium or Netherlands to pick you up some: it's readily available in the supermarkets there, and dirt-cheap too.
It's bottled in Belgium and is quite easy to find there. Delerium Café (of Tremens fame) has it on draught. FWIW It's sweeter (less bitter) and has less diacetyl (butterscotch) than FES, and the loss of complexity makes it the inferior beer as a result.