Halfords where I am dont stock Alpine adapters but if they did the bloke told me that they would cost in the region of £70!(shocking)
Phoned autoleads who said there was a new adapter coming onto the market which works with Alpine, Sony, Kenwood, Panasonic & JVC (universal basically) in the next couple of weeks. They then put me in touch with a local ICE dealer here in Swansea who will sell them for £35!
My advice - dont get ripped off, wait till the new adapters are out!