I've been searching high and low.
Now, that was a task! And it really changed my perspective and attention. My first thought was to search for foliate heads in ancient Roman remains, like the arch You mentioned, mwyalchen. Either my senses are not very sharp - and my eyesight is indeed limited -, or the guy is hiding very well. I made some pictures of several arches - Septimius Severus, Titus, Constantine - but unfortunately without telephoto lens.
In Ostia antica I had a close look at some details of architecture or sarcophagi - masks I found, but foliate heads ... I wouldn't trust myself no more than a learned person's book, so I still don't claim the absence of foliate heads in Roman antiquity.
Let me show You some pictures:
The only green man I found in foliage, was this one:
Resemblance to a foliate head I found in the Colosseum:
And ... ah yes: the plague we've been talking about!
No pentagram, but a compass.