I forget, are you in London or somewhere else in the UK?
Pet Pavillon has them and they call it pizzle sticks. I think that's the only pet shop in London that I found with them...no one knows what they are there LOL I thought that was so bizarre.
But we always grab them from there, they're really stinky but last a long time and the quality seems good.
I don't know whereabouts you are but if you have a Pet Pavillion around, might be worthwhile to give them a call and see if they have them.
And they're hard and as the dog chews it, it doesn't break off in chunks, instead it turns sort of sinewy....and it cleans my dogs' teeth pretty well. It's all edible too and I haven't heard about it causing any problems like hooves, pig ears, raw hide, etc. We absolutely love them for all our dogs.
If you have a really aggressive chewer they don't last very long though. I usually give for about 20-30 min and take it away.
EDIT: Nevermind LOL I see you're in Wales...I don't know which stores are there haha