How to deal lightning damage with a tempest domain cleric?

Tempest domain clerics get the following feature at 6th level:

Thunderous Strike. At 6th level, when you deal lightning damage to a Large or smaller creature, you can also push it up to 10 feet away from you.

I’m a bit confused as to how this is useful. As far as I can tell, there are no ways to deal lightning damage to enemies as a normal cleric and tempest clerics get a single spell from their class spell list that can do it, Call lightning. And while that is not a bad spell, it seems weird to have a class feature for a single spell.

So what are some other ways a pure tempest domain cleric could deal lightning damage? Any magic items? From the race? Something else?