Availability calendar for renting personal website

We have a personal website made with iWeb (Mac OS) to advertise an flat we rent on the sea side. We have integrated a free availability calendar on it but it doesn't work properly. We need someone able to provide us this functionality so we can integrate it in our website. The sole constraint is that we need to be able update this calendar externally (the admin part is not part of the Website it self) and then put some HTML code in the iWeb page of our renting website so that the calendar (non editable) is shown in our website. We don't need to provide the users the ability to book the place but just to display a simple calendar with availabilities. So we need a simple interface where we can manage this calendar (basically determine the dates when the flat is available and not) and then it displays a statuc calendar on our website (yearly view with red day = non availabile days and green days are available days).