Don't remember the date, but wasn't Admiral Vernon's ill-fated seige of 
Cartagena around this time, and didn't the British produce medals commemorating 
this "victory" in advance?   If i recall, the governement had to confiscate 
them all to avoid embarrassment.   Perhaps those buttons were pro-British 
and could no longer be used in the UK after Vernon's debacle, so they were 
dumped in America on a population that was even more patriotic than those in 
the motherland at that time (1740s). 

 Phoenix buttons of the early 19th century are an interesting analogy. Made 
in the UK for the army of Henri Christophe of Haiti, the tyrant was 
overthrown before delivery, so the enterprising Brits traded their inventory on the 
Pacific Coast, where buttons with French inscriptions were still considered 
the height of fashion in revolutionary circles.   There was certainly no 
martket for things French in Europe after Waterloo and especially not in the 
UK.   Caveat emptor!

Bob Hoover