I confess that I found mine via Amazon zShops, but various pilot shops offer a supply service for new-original POH, try Transair and AFE. I'd expect to pay around £70.
Or just copy the flying school's, which may possibly trangress copyright law, but on the other hand everybody does it and it's unlikely to offend anybody so long as it's used for the intended purpose.
Not the official document, but AFE also do
a rather nice pilots guide for £13 by Jeremy Pratt. I like Jeremy's books, my only complaint being that he never includes emergency procedures - presumably for liability reasons.
A certain PPruner also occasionally has useful such things on her eBay shop (and check the rest of eBay whilst you're at it - they occasionally appear).
G