I had the same problem a few years ago. Tried all the local locksmiths and none had the correct blank. I eventually got them from ECSmith on the internet. However a couple of weeks ago I needed a couple more keys. Tried the internet and horrified at the price and in a fit of desperation (purely because I was passing the door!!) I called into my local locksmith, not expecting any success. Apparently the blanks have only recently become available, and at £5 each a bargain. I would just persevere and try some more locksmiths.
Mike 😆