For international parties, they could be anywhere! haha It usually depends on the organizer. I would say they’re most likely in popular areas like Shinjuku, Shibuya, Roppongi, etc.
In my experience mixing with locals, it can be kind of terrifying for them if you approach them first. If I was in a bar with both locals and foreign residents/tourists and I let others come to me it was less awkward. Just beware of creepers!