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I don't think that's much of an issue DBI - after all, UK runners use travel agencies to do overseas marathons. There's an overseas ballot as well, run separately to the main ballot. At Boston several runners mentioned how hard it was to get a entry for London - I imagine that the overseas ballot is at least as oversubscribed as the UK one, if not more, and there's no equivalent to GFA available to overseas runners, unlike some of the other majors.
I notice that the VLM website only lists one Tour Operator in the states and none in Canada, but plenty in other places.