I just went to a really great place yesterday. It's just over the border from Herefordshire, and it's called Hay-on-Wye. It's renowned for its bookshops, and boy does it have a lot! If you've ever been in one of those shops that's stacked solid, floor to ceiling, and somehow seems to be three times the size you thought it could be from the outside, then imagine a town with dozens of similar shops
Anyway, I've already got an early edition of Ian Watson's Inquisitor (later republished as Draco), and yesterday I picked up Chaos Child (for about £2.50). Unfortunately I can't find Harlequin for anything less than about £15, with most being £30+!
On the plus side, I did also get hold of three of the Gotrek novels (Trollslayer, Skavenslayer and Orcslayer - yes Orc isn't a William King one, but it's still Gotrek) and got change from a tenner for all of it, including Chaos Child I now also have a full shelf of Warhammer novels in my own house