Not positive how complete and accurate the online ones are, presumably pretty good. However, you used to also be able to get a list at city hall in MK. They had a list for each park plus one for resorts/downtown.
We weren't too scientific about which ones to get - looked for them whenever someone was waiting on part of the family to a ride one was too short/scared for; would check for nearby locations whenever we were sitting for lunch or a snack break; usually got one from a favorite ride, resort we stayed in, resorts we visited. If I recall, seemed like a lot of resorts had pressed quarters instead of pennies, so that requires 4 quarters fee plus one quarter to press.