Thanks, but both of those links show exactly the same thing I was referring to.
They both give a part number for the tensioner assembly, but not the individual pulley.

After some further searching I have located this replacement part: REPM317402.
And there are a number of very reasonably priced sources for this pulley ($15 shipped).

So I have ordered one of these, and will let you know if it silences my rattling noise.
Thanks.