Im not gonna go into legallity, its all bullsh*t lol, and nobody ever agrees on if theyre right or wrong.
To answer your question, go with 5800-6000k.
Its a nice colour, is plenty bright enough and is the one your most likely not to get issues with the police with.
I have hears that 8000k reflects off of raindrops so is useless in the wet.
Where from? Go to ebay and search for londoncolour. I bought mine probably about a year ago, and so have plenty of members since. The kits arent the cheapest on eBay but they are by far the best.
Dont get those £20-30 kits, they are mostly from far off countries and if they break, which alot do, your have all sorts of issues returning the faulty part. Londoncolour is a UK seller.