I agree that 1960s WMS EMs are hard to find.
That is part of the reason that i have sought them out
and my collection has a very heavy dose of 60s WMS EM pins.
There is one that i am still waiting to see in the flesh
and that is a WMS Whoopee (4P),
its not that they are that low of production (IPDB says 2075 units),
just have never seen one in person.
WMS Reserve is also kinda rare, only have seen my buddy Sam's game.
The GTB EM pin "NOW" is kinda rare, seems most are European re-imports.
Also do not see many Bally KickOff/Quarterback pins.