Other than going directly to HP, I think your only real option would be to try and find the same/similar model refurbished or offlease, preferably stripped down. Which you can then use your old units parts in. I saw the DV7s in similar configurations being sold used for around $600-$700 on eBay. There are many Laptop outlets though, you'll have to google them.
I did find this one place seeling just the motherboard.http://www.sparepartswarehouse.com/HP,Pavilion,dv7-1000,FS148UA,Laptop,System-Boards.aspx