40 inch TV? Just buy a new one. Even if you could get a board, no guarantee that would work as a fix, or that whatever took the board out wouldn't just blow the new one. Unless you have clearly identified the problem I wouldn't mess with it.
If you really wanted one, try finding a TV with a broken screen. Fairly common to find parts only items for sale on Ebay.
I'm seeing prices as low as $200 for some off brand 40" models.
Now if this TV was more like $800 and up, and you could get a board for a reasonable amount, then maybe.