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There is absolutely no problem to shop on the British online stores. The shipping to US by Royal Mail is not cost too much and sometimes it's free. The sites like probikekit.com and others specifically working on US market and, for example, tires are cheaper there. So, there is no problem to buy specific 'British' parts.
For me it looks like the small cogs has slightly bent teeth. Also, how you measured your chain stretch? The bike is not looks new and chain has no oil on it. It can be a situation you using small front chainring and small cog and they just wear out faster then other cogs? If chain stretched out it skips on your preferred cog first and works fine on others.
I would like to add one more point: the important part of the question is a general fitness level and/or age of the rider. Does rider more sport oriented or not. General people my be hurt by sport bike's lower body position, wile for fitted young people the cyclocross bike is a best answer.
