Almost any similar era monitor will work. It is not MDA/Hercules, that runs at 18.432KHz, but a CGA will even though it is colour.
A BBC, Electron, Sinclair etc monitor will work but they are composite sync and video, you need a chip, an LM1881 from memory, to split the sync signals from the video. But you might find that feeding the composite signal into all three inputs might work, or will need a signal level boost for the syncs.
Otherwise monitors used in many test equipment such as logic analysers, network analysers etc might also work. These were two a penny years ago, I still have several to bin. Where are you?