Reviving this thread to say that from the Martin Lewis email this week, I found out that you can buy cast albums online at Oxfam: www.oxfam.org.uk/shop/music-films-video-games/music. Search under "soundtracks" (yeah, I know) and there are a fair few recordings, scores etc.
The Royal Court now has a Samuel French bookshop and small coffee shop upstairs but I think it might only open just before and after performances. Lots of choice of play texts and theatre-related books, though. I even got a signed copy of Antony Sher's "The Year of the Fat Knight" there late last year.
I recently bought 4 out of the 7 hardback Methuen Drama Modern Plays 1959-2019 there, and I couldn't find those on Amazon to buy individually (in hardback, that is):
Shelagh Delaney's "A Taste of Honey" (bought) Edward Bond's "Saved" (bought) John McGrath's "The Cheviot, The Stag and the Black, Black Oil" Caryl Churchill's "Top Girls" (bought) Sarah Kane's "Blasted" Kwame Kwei-Armah's "Elmina's Kitchen" James Graham's "This House" (bought).