Best place to start is the UK agents for MKS, at www.zyro.co.uk. Doubt
if they do private orders, though, so you'll have to place the actual
order via a bike shop who deal with Zyro.
Avon Valley Cyclery source a set for me from Airnimal. They looked
really nice; however, they are NOT SPD-compatible which is a pain. If
you already have an investment in pedals and shoes then compatibility
really matters.
I had to revert to my existing home-brew removable SPD solution.