The current version of the Unity ports of Doom and Doom II has the IWAD easily accessible in the <game data>\StreamingAssets folder and the WADs for the curated add-ons can easily be found in the user's profile folder under Saved Games\id Software\<Doom Classic or Doom 2> folders since the Steam update for them.
Topic on Talk:Doom II: Hell on Earth
Yeah, but Unity IWADs are the censored ones and add-ons aren't really compatible with source ports and can be buggy sometimes (also, those got some censorship as well), so that's why you need Unity2Classic. It doesn't only extracts those add-ons, but it also downgrade's 'em to the older versions, which are more compatible with source ports and aren't censored.