MatrikonOPC Simulation Server is free and it includes MatrikonOPC Explorer, which lists proper names of available OPC servers.
Once you connect to any of the servers then you can click on "Add Tags" which should list all available tags and show their proper name usage (in the attached picture you can see an example tag that was selected as "Boolean" from "Random" folder but has name Random.Boolean which you would use in one of the PLCAddress properties).