I want to replace the camshaft drivebelt, but cannot find the correct replacement part!

The Volvo dealers, etc, here in Birmingham, UK, say a 125 tooth belt is correct, but they are too short! The one on the car has 133 teeth, or thereabouts!

Can anyone tell me what is going on here? I really need to replace this drivebelt, as I don't know when it was last done.
Thanks, to anyone who can help me.
Jim