I added quite a few second-hand shops in the UK (mostly England, but also one in Scotland). There are some non-music specialist shops, but they have significant sections on used sheet music.
I also changed the layout a bit to make it more eye-candy and more easy to use.
I copied the table from the Music Publishers page and change it slightly. I also added a custom ToC, as by using the table instead of headings the ToC was lost, but the function was useful so I replaced it.
I was thinking that in order to leave more space (and thus make the entries look nicer, especially the phone numbers and some addresses), it would be better to either reduce all links to a "link" text, and that would be a hyperlink to the actual site (so the "website" column would be a lot smaller than it is), or alternatively, for the sites that have a website, we could link the name of the shop to the website (just like the Music Publishers page, in which the names of the publishers which have a page on IMSLP link to these pages, while the others don't).