Hella have a list of dealerships around the uk on their site. I think you can get them from tps or andrew page places or even off ebay pal.
Part Numbers i bought for RHS versions are 1LL 009 476-031 and -041 so that might help if you have a butchers on ebay maybe, or if a local dealer is better for you mate.
Probably another stupid question but am I right in thinking the HID kit has some sort of rubber grommet so you just drill a hole in the back of the headlamp cover and feed it through there??