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Get one set of a 1000 results with a straight search. Then get a sowewhat different set of 1000 with the same search by asking for pages updated in the last year. Repeast with a couple of other advanced settings.
If you are using the API, then deduplicate the various SERPS and you have (usually) over 1000 results.
Again use Advanced Search, but this time use "[only] return results from the site or domain" to restrict yourself to .com. That gets you the top 1000 for .com alone.
Repeat for .org or .co.uk and all other TLDs you are interested in.
By doing an unrestricted search too, you can approximately correlate the sets of results (I don't expect them to match 100% because the various SERPS will have come from different data centres) to say that (say) the 300th .org result would have been just outside the top 1000 of the unrestricted search.