Craig, MDC in Derby stock the Gunze range of acrylics, which in clude USN colours, see link below:
http://www.shopcreator.com/mall/modeldesignconstruction/
They should be quite close to you.
I use both Gunze and Tamiya acrylics as they can both be thinned with Tamiya thinner, however I find the Gunze range has a better selection of dedicated colours, i.e RLM, USN etc.
Karl