They aren't cheap. Cost me £90
Got them from here:
ultimate ear protection | Hearing Protection | Ear Plugs | Hearing and Ear Protection Manufacturers London UK | Best Ear Plugs
They had a stall at a bike rally I was at a few years ago and I was really impressed with the product.
The plug is made from a mould of your ear canal so it fits perfectly. Not like trying to jam in those cheap foam ones you get.
They have a local audiologist in Dundee who was able to fit them for me.