I love ads in music magazines in general – the things you find in old 70s Melody Makers, NMEs, ZigZags, Creems, etc (which I've been poring through the last few years for the glam book)
C.f. Lester Bangs's fantasy of owning a huge tunnelled labyrinth of stacks in which were stored every record that ever existed - which now exists for everyone, it's called Spotify / YouTube/ Internet - my update of that fantasy would pertain to what remains still stubbornly material and un-digitized, which is the bulk of the print-and-paper music press pre circa 1998.
(Although I hear there are moves a-foot to digitize the IPC back pages in toto, which is a good move, and various searches and Googles will dredge up great swathes of things - many years of 1970s Village Voice, for instance, with all the small ads and box ads for concerts etc, as well as the reviews and features).
Yeah, a giant room - a maze of rooms - a building even, a back house - that contained most every music magazine that ever existed (well, Q I could probably do without, and Rolling Stone after 1978 probably), every zine....