We had a similar problem with one of those keys.
After our local key shop couldn't provide, we went into Plymuff and into a national chain (Timpsons) and the price was stupid expensive,
HOWEVER, across the road there was another Key cutting, Locksmith/cobblers called "Cobblers and Keys", 2 Market Way, Plymouth PL1 1PB Tel 01752 257257 www.cobblersandkeys.co.uk/
They did the job, there and then for less than a £10.
Give them a ring. First Class service
NB. For some reason, the above message says the name of the shop is Shoemakers and Keys. This is wrong. It is called Cobblers and Keys but, for some reason, it will not accept an edit. It fact, when I go into 'Edit' it says 'COBBLERS'. Is this computer trying to tell me something.
Sorry Andy for not replying earlier.
Yes they are numbered. I thought I might have found them on the internet and just ordered a replacement by the number. Unfortunately, I can't find out what they are called so searches just keep coming up with the conventional replacements.
Quote from Wikipedia;
A tubular key (sometimes referred to as a barrel key when describing a vintage or antique model) is one that is designed to open a tubular pin tumbler lock. It has a hollow, cylindrical shaft that is usually much shorter and has a larger diameter than most conventional keys.