You can search by custom fields. 
You can make them searchable in the settings:
You can also include them as columns in the directory too (which means you could sort them by clicking on the column header):
And an example of a search:
You do need to wait for the Jobs::ReindexSearch background job to run [1] to include them, but you can speed that up by triggering it from your /sidekiq/scheduler page if you have access to it.
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which could take up to an hour ↩︎