The easiest way to get charging items is to request them from your in-game friends. On the ipad, you look in the collection list for the collection that requires that charger, then hold down on the charger icon until a dialog box pops up. The box will have a button for "Ask Friend" and then you can choose a friend to ask. Make sure your friend has a high enough level as required by the charger.
If you do it this way, your friends can give you a charger and it doesn't count against the 50/day limit. Also, giving a charger doesn't decrease one's inventory of that charger.