I've decided to gather some patents after searching for fun but there are some interesting patents that have been approved and could've been manufactured. Here are some of them.
GE Duplex Mercury Switch and GE Combo Device with Mercury Switch
Hubbell Mercury Switch
Bryant Mercury Switch with Exposed Contacts (I'm assuming under the BECo Name)
GE Specification (20 Amp?) Grade Mercury Switch
Pass & Seymour Pre-Cursor to the Grounded Receptacle(?)
Very Early GE Grounded Receptacle
Sierra Biplex Grounded with Light Panel
Sierra's Version of Despards]
Sierra Grounded Triplex Vertical
Sierra Grounded Triplex (Horizontal)
Pass & Seymour Multiplex Triple Grounded (One on eBay!)