Abraham supplied a JSON file with the SMuFL version of Cadence, so if you bought MTF-Cadence, you should have the JSON file.
Back on topic, Overture hasn't been updated since 2019. Don Williams has supposedly been working on Encore 6, which is due to be released in "Late Fall 2022"...
He isn't responding to questions on the forum, and no one knows whether he's 'active', in any sense.