UK Oxbow Cavy Cuisine - Where to buy?

I've read that Oxbow Cavy Cuisine is better for guineas over 1 year old than Supa Guinea Excel. But I can't find anywhere to buy the Oxbow from! The only UK online shop I can find says you have to be 18 to register so you can buy, and I'm nearly 16 so that's out of the window. Does anyone know where in England I can find this stuff? And what's the best way to introduce a new food into a g-pigs diet, such as changing the pellets to another type?

Also - which type of hay is best for pigs aged 1 yr and over? I've just been buying meadow hay up until now...what do you think?

any help would be much appreciated!!!