Some people cut down VCRs, and their RF gear is often better than what is available these days.
Anyway this guy
covers some of the things out there.
As for internalising things then what voltages does the transformer of the TV produce? Quite often they will have a lower voltage rail that you could convincingly run a modulator from, and there is usually a fair bit of space inside those old boxes. That or you could tap the mains and run a USB charger or something to give whatever you want 5v.