Figured I'd make a larger post for you and anyone that was interested. Like I mentioned in your post, I did make a calculator that would let me find the best coverage options available. I initially wrote it for in-game team movesets by allowing myself to specify what types I want and what types I had available. For example, if I had Dragon Claw and Earthquake for my Garchomp, should I run Iron Head or Poison Jab as my remaining third move and keeping Swords Dance as my fourth.

I initially had Ice, Fighting, Ghost, and Ground as my best output. Which a few Pokemon can achieve. Nidoking was the first one that came to mind. I had also not included any combos that had the same score, so it only printed the first one. So in addition to that, [Ice, Ground, Fighting, Flying] and [Ice, Ground, Fighting, Dark] both also gave me the score of 32. Freeze-Dry was not on my mind at the time, but by allowing that as your ice move, you can get a score of 33 instead.

Types: ['Freeze-Dry', 'Ghost', 'Ground', 'Fighting'] (Uses unique move: True)
Types: ['Freeze-Dry', 'Ground', 'Fighting', 'Flying'] (Uses unique move: True)
Types: ['Freeze-Dry', 'Ground', 'Fighting', 'Dark'] (Uses unique move: True)
Coverage Score: 33.0

Unfortunately, from what I can see, only Articuno would get STAB on two, but lacks the other coverage types.

One notable one which was mentioned already in that same thread as a reply to my post would be Kyurem who can run Freeze-Dry, Earth Power, Focus Blast and Shadow Ball. I think there was some mixed physical/special combos using these types, though. Like Mamoswine with Freeze-Dry, Earthquake, Throat Chop/Knock Off and Body Press (lol.)

As far as Electivire himself goes, I forced using Electric as on of the four types. That gave me three combos with 31 score.

Types: ['Electric', 'Fighting', 'Ground', 'Ice'] (Uses unique move: False)
Types: ['Electric', 'Fighting', 'Ground', 'Flying'] (Uses unique move: False)
Types: ['Electric', 'Ground', 'Fire', 'Fairy'] (Uses unique move: False)

So unfortunately it seems the best coverage types are still the ones he already had.

I am aware of Pokemon DB's calculator as well, this was just something I threw together for my own personal usage and was able to apply it to this fellow's post.