1) There do exist tapes of his playing, but these are not publicly distributed.
2) Buy Habermann's recording: "Sorabji: Legendary Works for Piano." It contains, on the first disc, a selection of early works by the composer eg. Fantasie Espagnole, and the Trois Pastiches. The second disc contains the three nocturnes: "Le Jardin Parfumé, Djami, and Gulistan". The third is titled 'Assertive Works'. This CD also includes the first two movements of Opus Clavicembalisticum. The only bad point is the piano has a really horrible tone, particularly on CD1.
3) If you are desperate to hear a recording get the Ogdon. Stay well clear of GDM's recording. Your best bet is to wait until Jonathan Powell's eventual recording. I wouldn't advise listening to either currently available recordings of the OC until you're completely familiar with his musical style.