Just about any schooling fish will work for a while, until the festae get big enough to scarf them down. I have used lemon tetras with young festae and ornatum.
or Columbian tetras if you'd like to be more geographically correct.
If geographical correctness isn't important to you.
For larger festae, I use Tilapines,
I wouldn't use buttikoferi or mariae because they are too aggressive, but prefer the less aggressive types such as zillii or Saratherodon linnelli. They are fast, and can take some abuse, without retaliating.
Here are young zillii, I believe they are available in Chicago from guys in the gcca
and linnelli, I put some of these with a shy female festae that refused to eat, and she almost immediately came out of her shell, and gobbles food like crazy with the greedy Tilapines.
the once shy female below