I think it's a lost cause. The only panels that looked similar (but without datasheets, so you can never know) were on Alibaba. From $25 to $50 a piece. Do not expect anything cheaper than that. And sure, one at $25 would be half the price of Adafruit's (or Farnell's) ones, but without any documentation, is it worth trying to save $25, at best, while possibly getting something that won't work?
Do no expect this kind of panels (7", 800x480, RGB interface) to be particularly cheap anyway. Those are relatively uncommon these days, and have been largely replaced with ones with either MIPI or eDP (for larger ones) interfaces. Even the resolution is not that common anymore.