It was available on release of the game. The Collector's Edition has sold out from the
Larian Vault, though. You can try online (amazon.co.uk currently has one copy of the regular edition listed by an affiliate, for example).
BTW the retail version of the game is Steam (if you can find it, the CE version includes 2 keys).
From kickstarter update #60, about the Collector's Edition:
The English edition is available worldwide exclusively through the Larian Vault.
IMPORTANT! There are only 1500 English versions of the Collector's Edition available; the rest is reserved for our Kickstarter backers. We aren't planning a re-print (the organisational acumen it takes confuses and frightens we developer-types), so get your loot while it's available.
A limited set of German, French & Polish editions will be available via retail.
In the Benelux, a limited amount of English editions can be found in Game Mania
No other editions are planned
