[CoryG89]

Perhaps it's possible to limit the search space by also looking only at experts likely (or possibly) have worked with the US government or NSA in the past or present. Then maybe you could get the list down to a reasonable number? For example, any experts that have never been to the US for extended periods of time can probably be excluded.

[zigzigzag]

How would you know? I've encountered at least one person who was without a doubt ex-GCHQ but didn't identify that anywhere.