I found a cable, it's a PHILIPS CM8833 MKII RGB MONITOR SCART ADAPTER CABLE
The CM8833 is the same monitor as the 1084 so in a few days I have my setup complete:
Supergun, 15khz RGB monitor, neo geo controller, power supply, volt display.
I'm really tempted buying a classic home computer now that I have this monitor, but it's better just to wait a little

I need to sleep sometimes