Hey!
There is a Finnish store that has these in stock, however you face multiple complications. Just to get it out of the way, I don't live in Finland, but managed to get one from them.
http://www.verkkokauppa.com/fi/produ...elin-ostajalle
Steelbook itself isn't sold separately, you have to buy Rayman Legends game and steelbook comes as a bonus if you wish. I personally ordered PC game which was the cheapest - 20€. So 20€ for PC game and steelbook, great right?!
Well, no. Shipping to UK might be expensive if possible at all. It cost me 15€ for shipping, but without going into details, it definitely won't be that cheap for you. But assuming they do ship and the cost is acceptable, credit card details and off we go right?! No no, stop right there! They don't accept foreign CC or Paypal so you have to pay via money transfer which can take like a week.
I still urge you to contact them at
myynti@verkkokauppa.com if you can't find it elsewhere. Worked for me, maybe for you too.
Good luck!