You really need to remember that even a 1 minute loop, if done well, can make hours of interesting music. A track over 4 minutes in a game is unnecessarily long. 8 to 10 minutes? Unheard of (even ambient music in games is only like 4-6 minutes tops).
I highly recommend you revise your time request.
In addition, as mentioned above, interactive music is not a bad idea. This is done by, in one method, having a base loop (say, 1 minute long) with basic instruments. Then, when new areas are reached or at certain points, other parts that line up with that loop come in, creating variation. This could be done for hours, weaving a unique, ever-changing score, custom to the situation. Although these scores are not common in indie settings, the're fun to do and you might find they fit better the mood you want. :)
I urge you to also check out some artists around Newgrounds- if you find one you like the sound of, shoot them a PM. It's a very effective way of finding good composers, as not everyone reads the forums regularly and that perfect composer might not be reading this.