I'm in search of receptacles that little were made of even though they are a common type. I want to get a hold of these for my collection.

Slater Ungrounded Duplex or Any Art Deco Slater Receptacle or Switch
Slater Art Deco Things are very rare and rarely appear. I've never seen any on eBay except for a switchplate. The lack of quantity make these rare.
Hubbell Ungrounded Duplex
Same reason, but the universal duplex is more common than this which is a surprise.
Australian Style and Universal Combo
These are very rare to get a hold of anywhere in the US. They were phased out after the Art Deco Era and there are only two known manufacturers so far, Slater and Hubbell.
Any perpindicular Receptacles Without a T-Shape on either side with No Ground (Falls under US Perpindicular Socket)
Not much to say other than it's obsolete and it exists.