How did that work out for you? I'm in the same position. The publication says if you're in the UK, you should contact the local DWP office. That seems weird; you'd think HMRC would be in charge of this. Have you tried DWP, and did it work? Otherwise, I find the same thing you have: it's easy to find where to apply for a certificate that a UK person overseas is covered by UK national insurance overseas, but there seems to be nowhere to apply for a certificate that a foreign (US) person in the UK is covered by UK national insurance.
