One can find his prints for sale at the Old Truman Brewery market in Shoreditch on Sundays (where Your Humble Correspondent bought prints of the two above images).
Meanwhile, there is Banksy's ongoing exhibition at the Bristol City Museum, which is going until the end of the month. Entry is free, though prepare to wait up to four hours in the queue, and get there early. It's well worth it, though; Banksy's animatronics, for example, are superb, and his oil paintings and other non-stencil pieces are excellent (the large oil painting of Parliament occupied by chimpanzees, for example, is splendid). I had occasion to see it recently; my photos are here, though they don't quite capture the works in all their glory.
(According to The Times, Banksy charged the Bristol City Museum just £1 for putting on the exhibition, on the condition that all CCTV footage that could identify him was destroyed. Also, only four staff were informed of what was being planned (the rest were told that filming was taking place). Given the level of technical skill in his pieces, I suspect that the reason Banksy is so keen to keep his identity secret has to do not so much with fear of getting caught for illegal graffiti as fear of being outed as working for The Man; I wouldn't be surprised if his day job was in advertising, film production or similar.)
Finally, French street artist Invader (i.e., the chap who sticks tile mosaics of old-school video-game characters to high surfaces) is exhibiting in London until 17 September.