I tried quite a few approaches. I went to ASUS' Twitter and Facebook pages, from which I got lazy responses.
I got a much more energetic response from contacting the ASUS "CEO's Office" at https://www.asus.com/us/support/article/787. They offered this diagram unprompted:
(Though while they've sent me a lot of messages, last I heard the part's department is 'looking for' the screw.)
Thank you for the kind offer, JBish, but a this point as I mentioned upthread I switched to superior aftermarket heatsinks, so the only reason I'd like a replacement is in case that changes somehow. I guess what I'm thinking is that there's no need for your extra to become my extra.
ationfictons wrote:That's a very interestingly-phrased question.
I've got to wonder how much it's cost Asus just to avoid sending you that $0.03 screw. Ditto for their refusing to send me a chipset fan replacement.