^ ah, ok, I was just about to say "guitar guitar", lol. i see you already got it. Guitar guitar is about 3 miles out- it's pretty easy to find, it's on the main corstorphine road (towards the zoo) or at least, it morphs into "st john's road" or some such lark.
sound control is def. worth going to- if even for the fact that, since you aren't there often, you can try out stuff that you woldn't normally try in your local shop, since they don't know you. the grassmarket is just down the side of the castle- head up the royal mile from north bridge, then take a left then quick right at another bridge (george IV bridge? maybe), that'll lead you down to the grassmarket- sound control is at the very bottom.
other than that,
www.yell.com can be quite handy for finding guitar shops, and it normally has maps too.
:drink:
EDIT: i haven't been to scayles though- it was just across the road from my sister's flat when she was at edinburgh uni last year, but I was always at her flat when scayles was closed... :( i think it's on st. patrick's square or something like that.