That shower mixer you have is an Elkay mixer.
If what you are trying to do is stop it from dripping out the showerhead then replacing the cartridge will do the trick.
You can get a new one from... http://www.arpny.com/
Click on "Single Lever Cartridges" to see the catalog and get the number.
If you are looking for trim to make it look like new post back... That's probably a bit more difficult.
You cannot mix and match in the world of tub/shower mixers. everything is brand and model specific. If you are remodeling this bath an upgrade replacement may be in order.