LBS as trying to order a single one is a nightmare as cost would be £2 - 3 but finding it will raise it to a lot more, from the myriad that there are. Desigend as a sacificial part so should be available from a B2B part. Just make sure you tell them what groupset you are running.
its a number 53 hanger, i needed to replace mine on a 08 vanquish and when i took it into halfords the system ordered the wrong one , make sure they order you a 53 if you go in as it was the second choice or get one yourself.
I never found it a problem ordering off eBay. Search for gear hanger and you will find companies that show front and back photos so you can compare carefully before ordering. Yours is listed at £3.99 delivered. Always worth ordering a spare as they are very light and easy to replace and do bend easily.