Interesting looking, not double roller as was reported, and not harness buckles.
The double roller military equestrian harness buckles are impossible to find, even from military specialists in these things.
to me it looks like the prongs of these may be stamped, and may not be very strong. I'd have to see them in person.
Personally I think they used what they had on hand and not every jacket may have had the exact same buckle. We don't get a good enough view of the buckle in the movie to know.
The prongs actually are pointed, and not necessarily meant to pierce the leather, but to 'grip' it at teh back of the strap as the leather passes over the prongs and is put back through the buckle.