Phew, thank goodness for that. 
I'm joking. Your best bet is probably the manufacturer themselves. They're likely to have spares lying around as not every pair will come out the moulds perfectly and, depending on their quality process, might mean they have odd ones about.
I'm joking. Your best bet is probably the manufacturer themselves. They're likely to have spares lying around as not every pair will come out the moulds perfectly and, depending on their quality process, might mean they have odd ones about.