Bingo, we have confirmation that my hunch was true, the Order of St John was named after St John the Baptist, the original St John. The guy who lost his head when Salome asked for it on a platter. Like Jesus, St John the Baptist was a popular figure to draw, paint and sculpt in the middle ages. So Elizabet Hunter has many images to pick from. I'd suggest not using the ones that feature Salome with Johns head on a plate.
(I got all excited and started browsing my collection of religious images so I could offer Elizabet a selection of the ones I find more visually pleasing. I really wanted to see if Cranach had painted one of John with his head still on as Queen Eva and King Felix are having a landschneckt themed reign and I like both Cranach's depictions of this garb. Then I read some more about the Order of St John, hoping there'd be some good images I haven't seen before and found out I'm looking in all the wrong places.)
According to a paper by Dr Ian Howie-Willis who is a Knight of St John and member of the St John Historical Society, St John the Baptist wasn't the original patron St Johns Ambulance.
"The Order has always been called 'The Order of the Hospital of St John of Jerusalem' but in the early years the 'St John' in the title was St John the Almsgiver. This John was a Cypriot who became Bishop of Alexandria where he became famous for spending the church's wealth in aiding poor refugees. His boast was that 'I found the treasury of my church full but left it empty'. The early boast of (The order of St John) is it's pre-military days was something similar. The Blessed Gerard, found of the Order, and his brethren used to say that the Order existed to serve 'Our Lords the Sick and Our Lords the Poor'. John the Almsgiver was therefore an excellent role model for the Order.
Some of Gerad's monks disagreed, however. As their Hospital became more influential and powerful after they were reconstituted as a separate Order in 1113, they believed a more prestigious patron saint was required. And, so one Saint John was dropped in favour of another - the Baptist in place of the Almsgiver. In addition, after the First Crusade, the brethren occupied the former Greek Orthodoc monastery of St John the Baptist so perhaps this was less confusing for everyone." (Howie-Willis, 2010).
One of the few paintings depicting the original patron: St John the Almoner. Painted by Titian (1490-1576). Currently located in San Giovanni Elemosinario, Venice.
The St John the Almsgiver that Howie-Willis (2010) refers to may be the St John listed in Wikipedia as John the Merciful (died c. 610), Cyprian Patriarch of Alexandria. Also known as John the Almsgiver, John the Almoner, John V of Alexandria, John Eleymon, and Johannes Eleemon. St John (the Almsgiver) is commemorated on the 12th of November, (details). There are a lot fewer images of St John the Merciful than there are of St John the Baptist from the middle ages due to a number of reasons. 1) John the Baptist, as the original John and cousin of Jesus, is much more of a superhero character and is more well known due to his inclusion in the Bible, 2) the ultimate charity of St John the Almsgiver probably didn't sit that well with members of the church who were trying to accumulate wealth and power so I doubt they would have promoted his image and through this, his cause.
There are a number of easily searchable images from google that come up for St John the Merciful however many of the ones that look medieval are in fact modern icons for the Greek Orthodox church. Finding medieval images is going to be a challenge, especially finding an image that can represent the St John Ambulance boys at Rowany Festival. I really want to find one where he is giving alms to a clearly sick person.
Howie-Willis. I, 2010, St John the Baptist: The Patron Saint of the Order of St John, Proceedings of the St John Ambulance Historical Society of Australia, Vol 10.