In April, the venue I'm familiar with (Palm Beach International Equestrian Center) is wrapping up their winter season and most barns are leaving, or have left, to begin their preparation for the summer season.
Every year I meet several people from New Zealand who come with polo horses and teams. You may even be able to start where you are and come with them. And it seems that grooms jump disciplines frequently, going from the jumping sports to polo or visa versa.
Although you do get to see the country (which ever one(s) you go to), there is a greater emphasis on work and not much holiday. Regardless of discipline, 6 to 7 days a week is the norm. Long days, too. You may already know that, but thought I'd put it out there.
I don't know about the jumping crowd, but will say that we in polo love barbeques. At least once a week, everywhere I've been, people and groups host large barbeques and everyone is invited. Players, grooms, and families and fans.