I expanded my search to include some similar qualities like grace, charity, and gentleness, since I didn't come up with much for either truth or mercy! There still isn't a ton here, but hopefully this helps. (Also, for what it's worth, I like Verity a lot as a name in its own right.)
Alethea/Aletha/Aleta/Letha - derived from a Greek word meaning "truth"
Elvira - "all true"
Sanna - Swedish short form of Susanna, but can also be derived from Swedish word for "true"
Clementine & variants - merciful
Mercedes - mercies
Eir/Eira - means "mercy" in Old Norse
Eskarne - means "mercy" in Basque
Amara - grace
Charis - grace/kindness
Aglaea/Aglaia, Euphrosyne, & Thalia - The Three Graces/Charities
Sanaz - may mean "full of grace" in Persian
Ruth - just one letter off from "truth," and thesaurus.com has it listed as a synonym for "mercy"
Caoimhe/Keeva - beautiful/gentle/kind
Vieno - means "gentle" in Finnish
I love Mercy and Verity, they're both lovely. I love the option of Clemence or Clementine as well. I also think True and Truth both make beautiful options.
Verina/Verena, Verdad, Vera, Verona, Veronica, and Veronique are great options.
Alethea or Elethea are beautiful as well.
Mercedes, Grace, Honor, and Hannah could all be options as well.