I think finding a slaughterhouse for pigs is quite difficult. I've never seen pigs at Shotts but you could ask. Or contact Wishaw - we don't use them because they are so big. Shotts looks awful there but we find them good for our sheep, small.
There used to be a slaughterhouse in Galashiels which did pigs, but it closed after a wild boar seriously injured a slaughterman.
Otherwise it's further away somewhere down the M74 but I don't know where - sorry.
Hopefully someone else will come along with better info
Now I see you're actually asking about butchers - sorry