Hm. There are online figure drawing resources that have been made available for artists- try pixelovely, it's wonderful. Deviantart has a ton of nudes people have made available to the public but they're kind of terrifying. These livemodel pdfs are super high quality- you should pay but know that it took me a while to find an link that wasn't a straight download. You're not liklely to get caught drawing porn but it's worth the effort (and not that hard) to stick to images people have made creative commons or whatever. Just look up the licensing. If it doesn't say, assume it's copyrighted.
But why not just try to find another group figure drawing session near you? It's not usually too expensive if you're splitting the cost with a group. You're probably too young for it (they're mostly held in bars) but Dr. Sketchy's burlesque figure drawing sessions are really fun and happen all over- there's a lookup here. Usually pretty short poses though. Lots of universities/art schools/community colleges/arts centers will also have figure sessions, many of which may be open to the public.
You might get more ideas if you ask in the art forum. 6 hours is a long time even for a prone position and you'd probably end up breaking it up over at least three sessions regardless. Pixelovely gesture drawing will help you get faster.
Alternately, try to find a friend willing to let you take a photograph of them nude. Promise not to share it, and don't. Give them some money for helping you out if you can afford it.