I buy a 4.3 tft lcd screen. I take it from a reversing camera for cars (more details in the components list). The resolution isn't so bad. Anyway, old video games doesn't have 4K resolution. I keep the cable, it's usefull to test the circuit.
A thing to know : you have 3 cables. Red for the alimentation, yellow and white for the composite signal.
Screen power supply : 9-12V.
I found an AC DC Adaptator (from an old alarm clock). You can also use an Universal adaptator, or a lot of battery to test the screen.
The last thing to know : the screen turn on ONLY IF YOU ENTER A SIGNAL IN COMPOSITE (and the power supply to of course).