It's very possible that you'll never find a datasheet. Reverse engineering may be your best option for understanding what you have.
I recommend that, rather than dissecting a dead one - study a live one.
I would work from the bottom up. First find the LCD lines, look for meaningful signals. Use a logic analyser or oscilloscope to determine the type of bus and the shape of a transaction.
For example, for SPI you'd see a chip select, a square wave clock and two data lines. For RGB video, you might see three analogue ouputs with luma components. Or, for CVBS/Composite you might observe a colourburst.
Once you can take some action on the original device and predict the signals to the LCD, you can clone it.
Build a software implementation on your microcontroller to output the same patterns. Observe that it drives the LCD in the same way.
Alter the behaviour of your software driver repeatedly in small meaningful ways to discover how inputs relate to outputs. Try to determine the effect of flipping bits in the data and the effects they have, use this to guess at the data format.