If you drive up yourself on a weekday at this time of year and get to the visitor centre shortly after opening you should have no problem getting a tour. If the first few tours are booked up your nly 10 minutes drive from Drogheda town where you could go and see a shrivelled decapitated head if you fancy it, or else spin over the bridge to see Dowth. I'm pretty sure Knowth closes from the month of November on so you may want to hurry over there as it is unmissable for anyone with an interest in all things megalithic.