The two tokens shown below are the only two slot tokens I've come across. This excludes premium tokens. The ones shown are from Treasure Island, Las Vegas (1996), and Ballys, New Orleans (possibly current?). Both have plated centers and are one-piece tokens.

Has anyone seen one from another place that has $20 denomination and was playable in a machine?

The only $20 machines I know of in Las Vegas today are at South Point and they are Ticket-only multi-denomination machines.