A map of where it is allowed to collect oysters can be downloaded here, here it is.
The green circle indicates the approximate location where we collected, but you can collect anywhere that is not coloured in.
The oysters come out at low tide, so you need to have rubber boots and good gloves. Theoretically you may need tools such as a chisel, hammer and goggles, but it is difficult to collect oysters this way, so it is easier to just search for them on the shoals.