LHR still has an 'enthusiasts' shop although since the sad closing of the spectator's viewing area on the roof of T2 and the QB (and their subsequent demolition and replacement) it has relocated. It can be found on the western side of the Heathrow Airport Academy building between the Bath Road and Northern Perimeter Rd next to the Renaissance Hotel. There's a small covered spotter's platform as well overlooking the threshold to 500m of 27R IIRC.