Both Drakan Games have been out of production for nearly 10 years now and the PS2 version never got an essentials release or digital distribution e.g PSN. However boxed, original games do turn up at Amazon and ebay so those are the best places to look. I have sometimes seen them second hand local computer games shops but none of the usual high street retailers. Websites such as Game and Gamestop have used copies for sale too. If you look hard enough you can still find brand new copies!
I would strongly suggest that you DO NOT download Drakan from torrent sites as these can contain viruses and often have parts of the game missing that you would otherwise be able to enjoy by owning the original game. There are no legal digital download versions as far as I know. But yeah, Drakan is hard to find now. Pity Sony don’t release it on PSN – there has been some classic PS2 games on there and some re-remakes so they will work on the PS3.
Until hell freezes over or pigs start to fly, Amazon, Gamestop, Game, Fry’s Electronics or even Ebay are your best bet.
Here’s a link where you can buy the PAL version of The Ancient’s Gates in the UK @ Game. Amazon have plenty in stock too; here are the links: OOTF and TAG. OOTF tends to sell for silly money as it is a very rare game.
Sony’s official TAG game site is here where there is also a store / merchant locator where you can buy the game.