Front indicator bulb - where to buy?

Hi guys,

I have a 2011 C4GP with LED DRLs. One of my front indicator bulbs blew last night so as I was passing Halfords I popped in to buy a replacement. Their system told me to buy amber bulb type 581 (PY21W) so I did and merrily carried on my way home. When I got home I set about swapping the bulb to find that the bulbs are completely different. In fact working out which bulb type I need involved quite an extensive web search (even FAQ #47 on this website is wrong) and I've settled on an obscure type 433D amber BAY9S. Halfords don't look to keep these in stock (only the clear version) and I can't think where else to try except the dealer. My local dealer is not open when I'm near home and every other dealer near work or on my journey between home and work adds over an hour to my day.

Am I now actually looking for the correct bulb type and does anyone know where I might get one from other than having to visit a dealer? The amber version is definitely not common - even Auto Bulbs Direct only carry the clear version.