Nope, you can't. The only place I've ever bought it in the UK is from performance oils limited. Opie oils (cornwall) stocks it as well. Both do mail order.
I've been very happy with the stuff - my car has an oil temp guage as std. and the oil oil temperaures are 10-15 celcius lower than I was getting with Miller's synthetic stuff.
Previously it could hit 130-140 degrees, which is too high in my opinion.
The AMSOIL stuff stays in grade as well.