Any name brand synthetic 2 stroke oil is good, just make sure it is not "injector" oil.
Nominator and interceptor have given me more than enough satisfaction. Use 20 to 1 until you go through a tank or two and then you can cut back on the oil. If you don't know where to get it, you could try a motorcycle shop or a place that sells Lawn cutting stuff or boats.
Here is a link in the UK
AMSOIL 2-Stroke Oils