A local grip house would be the obvious answer, but that's going to cost some money.
Assuming you have little or no budget, and that it's a sunny day, there are a couple of ways to proceed.
You can back-light your group....that is, put the sun directly behind them. Early, low sun will be a problem. You'll want to do this mid-day...but not mid-day in the middle of the Summer. That is, you want the Sun high, but not directly overhead.
You'll need to find a dark backround to accomplish this....ideally, slightly darker than the group's faces. This technique works best with dark haired people who have hair.
Then, just open up the iris an extra stop or so, and make sure you've "flagged" off any sunlight from directly hitting the lens of your camera. Not the most elegant solution, but the cheapest.