The movie industry magazine Daily Variety has, every Thursday, a
complete list of all films known to be in current production. Any film of
sufficient stature to have Kate Winslet in it will most likely be listed
there.... though it is not infallible. Most large bookstalls and news
outlets in major cities carry DV and the Hollywood Reporter. It shouldn't
be too hard to verify.
And usually prop people have their famous 'notebooks', as well as more
than a dozen industry-specific publications, just for this purpose. And
most of the time they'd be a bit reticent to name the movie and the
principal talent right off the bat.... I thought this guy's post was a
bit naive, at the least. Usually they represent themselves as working for
such-and-such Production Company - sometimes you dont' find out the name
of the movie until much later, after the gear has been returned.
From having been in the movie business for 15 years, and from having
worked, prior to that, in two large Surplus companies who relied heavily
on prop rental, I never dealt with anyone who came off as Mr. Fox does.
YMMV
Cheers
John