Confounding Mists can push a City.

I don't see any rules to prohibit pushing cities, just nothing lets you, except Confounding Mists.

Is there any other way to push or gather a city?

Change them into something else then push/gather? 

FLOW LIKE WATER REACH LIKE AIR

*ahem* this doesn't technically push a city, per se, but with the elemental threshold achieved, a spirit can move 2 cities with their presence.

Bonus points for using this power on Thunderspeaker with Dahan in the land, as they can move their presence right along with the dahan.

Pardon the caps, I was excited because we found this card last night, and we used it to allow Thunderspeaker to drag everything out of one land into another land with even more things for a total of two cities, three towns, and various explorers in the final land. then Lightning dropped one of the major cards that allowed for 12 damage and ended the game for us at terror level 2.

I can't think of any other instances. The difficulty of moving Cities is obviously intentional.

(I see you have correctly figured out that Call to Trade has a misprint, and is Gathering a Town rather than a City.)

Flow like water, yes.  Forgot that can move cities.

Working on Ocean, and confounding mists is absolutely bonkers for Ocean.  Build that city inland?  Nope, you'll build it right here on the coast.  And then I'll eat it.