Right first off there's LOADS of places you can go mate.
I'm from the UK -there's loads of parties. Problem is in an all boys school you're not in the right social circle for it.
There are solutions to it.
For a start take up other activities. Get mates who are outside your school. Then you'll find out about the parties. You'll also get connected as a kind of social hub for your mates at the school when you invite some of them to come along.
Secondly, other places are many:
I don't know how old you are but pubs and clubs tend to be most peoples favourate haunts.
During the hours of daylight though try:
Coffee shops - GOLDEN, especially if they're near uni's/other schools (I presume schools too Uni's I know for a fact).
Malls - I was a bit skeptical about this but try it. Opinion openers there go down a treat.
Try taking up some activity likely to bring you into contact with a lot of girls. Do yoga, ANY kind of dance (ballroom, hiphop, jazz, tap, hell even ballet though it wouldn't be my pick). Well avoid breakdancing - there are few chicks in that.
Join a swim team (well it's maybie a bit less good at your age but most swimming classes for adults are 9 women 1 man).
Take up drama - tends to attract confident chicks. (and I feel like the girls that I got into the game to get when I say) confidence is sexy.
If you don't care about risking getting called up in a few years you could also join the cadets (or if you're at a private school, as seems likely, they have a special division called the Combined Cadet Force where you'll be an automatic officer => status).
Art is another chick magnet of a thing. Look for art classes.
Take massage courses.
The list is endless.
Anyone with any other good suggestions please add them ;-) some new places to scope out are always a fun days sarging.