The rule is the small buddies of Cityformers are Weaponizers. Barring the three obscure figures that were the first released TF toys and thus deserve to be special.
Scorponok has Fasttrack. But that’s it for Decepticons.
Hydraton was a Quintesson Cityformer, but he only exists in the novels for the Aligned continuity. No art exists, we only know he’s an underwater base who turns into a jellyfish robot.
IDW continuity gave us the Beastformer Chela the thunderbird city, but he wasn’t a Decepticon so much as one of Shockwave’s Maximals, making him inappropriate as a Decepticon.
Vigilem remains the only other option. He is a viable candidate, given he is evil, and has another name which can function as a Weaponizer name as Carcer while you could make a Deluxe or Voyager sized Liege Maximo to be part of him in city mode.
You could make the Nemesis into one. But the only time Nemesis was a Cityformer is the War For Cybertron games where he is just the shattered corpse of Trypticon forced to stay in ship form.
You could also do the Darksyde, but I can’t imagine making a city out of that shape.
Otherwise, you have to create an entirely new character or turn one of the cities the Decepticons claimed in the IDW continuity into one.