Looking at journey times and road distances, Stranraer aren't the furthest attendees in Scotland - Campbeltown travel 159 mi / 4 h in comparison to their 145 mi / 3h. I remember once trying to drive down the Mull of Kintyre and giving up halfway... Rubbish rubbish roads.
Not many places in the UK are further from their regional contest. Leaving aside Northern Ireland, whose bands are eligible to compete in the NW but never do, the only places that top 4h journey are various places in North Wales (Anglesey, Lleyn, and a little patch around Llandudno), the Isle of Wight (from Torquay), and a wide arc of Scotland that runs from the Mull of Kintyre across the middle of the country intersecting the East coast as far North as Caithness; very few bands lie beyond this - the Pentland Brass Band in Thurso, and the Kirkwall and Lerwick Town Bands in Orkney and Shetland respectively, none of whom have ever, so far as I'm aware, attended any contest anywhere. And of course, the Channel Islands, supplying our winner above, JPB.