Reserve a block of rooms for your guests at special rates at one or two select hotels with plenty of time before the big event. At most hotels, 10 per night is the minimum number of guests rooms required to make a block.
If you are holding the reception at the hotel or using any banquet space that number can be flexed. If you are looking for over 30 rooms per night, another good idea is to split the group blocks among two to three hotels. This way your guests can have a choice between different locations and prices.