That's a waterproof stagelight connector. Here's the cable on Ebay: https://www.ebay.com/itm/324426755355. I think the pin spacing is XLR standard, which is why these are somewhat uncommon (read: they're insanely dangerous to have lying around in a theater because they're possible to plug straight into a microphone cable).
If you're just looking for a waterproof bulkhead connector, there are some more standardized power connectors I'd recommend you evaluate first, such as Neutrik connectors which are explicitly designer power.
