Help! The Colosseum is all booked up, the tickets and tours, on the
official website until the end of July!
207mzh0324, see this on the coopculture website:
Every first Tuesday of the month :
June 4th at 3 pm (italian time): The pre-sale of tickets with scheduled entrance time for the ordinary access of the Colosseum, of tickets with scheduled entrance time to the Coliseum arena, in the monthly availability for July 2019 will be released both online and through the call center.
CALENDAR OF RESERVATIONS OPENING WITH GRADUAL RELEASE SCHEDULED ENTRANCE TIME COLOSSEUM TICKETS
Every day new tickets for the next day at 3 p.m (italian time).
Every Monday new tickets for the following week at 3p.m (italian time).
So keep trying for "ordinary entrance" tickets (these are the tickets you want if not interested in a tour) on these dates. It's possible tickets may even show up on random dates due to cancellations - although unlikely for a family of 5- so keep checking.
Don't buy the Roma Pass just for this as you now have to make a pre-reservation if using the pass for the Colosseum anyway.